![20 D A Y L I G H T I N G
the performance of a visually demanding task, but an increase
from 500 lx to 550 lx is likely to remain imperceptible.
There is some evidence that a lower illuminance is
required from daylight than from electric lighting, to maintain
a given level of performance. The reasons for this are not
certain: it is possible that both physiological and psychological
processes are involved. It is known, for instance, that
performance is better when the colour rendering quality of
the source is improved; the flow of light from a side window
is soft but directional, giving good three-dimensional model-
ling; it is also true that people prefer daylit rooms, so
improved motivation might be a factor.
The principal aim of lighting design is often taken to be
the provision of plenty of light. Possibly, this is because the
development of lighting technology has, throughout history,
been a search for increasingly efficient sources. It is also a
view reinforced by the fact that most standards use illumin-
ance, a measure of light quantity, as the principal criterion
of lighting merit. But to think in this way is to miss the point
completely: the purpose of lighting is to convey information.
The light that reaches our eyes varies in time and direction,
the result of interactions with surrounding surfaces. From this
variability, we are each able to construct a mental model of
our own immediate world.
It is helpful to think of our senses not as instruments that
measure energy, like photometers, but as receivers of signals.
It is then clear that the essential requirement with respect to
light intensity is that the illumination reaching the eye has
sufficient energy to carry the signal. This gives a theoretical
basis for performance/illuminance curves such as those in
1.14
Size, brightness and contrast are the three primary characteristics of visual
tasks that affect visibility.
1.15
The relationship between illuminance and task performance. The curves are
trend lines drawn through very scattered data.
Based on work by Weston [50].](https://image.slidesharecdn.com/5681580-250526183703-e4460715/85/Daylighting-Architecture-And-Lighting-Design-1st-Edition-Peter-Tregenza-33-320.jpg)
![24 D A Y L I G H T I N G
peripheral field can enhance or distract from concentration
on the task. Rapid movements and flickering lamps interfere
with performance. Conversely, a task environment that
conforms to expectations, that is ‘normal’, is supportive.
Daylight, with its variability and the information that this
gives, is part of what is ‘normal’ in many room types.
Brightness adaptation
The human body is able to change physiologically as the
immediate environment changes. When conditions cool,
the blood vessels near the skin rapidly become constricted
to minimise heat loss; in hot conditions, they dilate, and the
skin perspires, to maximise cooling. There are also long-term
physiological changes that occur when a person goes to live
in a warmer or cooler climate.
The eye adapts to motion and to particular shapes, to colour
and to brightness. These latter two are particularly relevant to
daylight. Over a period of an hour or so during a calm sunny
afternoon, the light entering a window may fall to a quarter of
its initial amount and its colour may vary from a cool blue to a
warm white; but, even if you are sitting working in daylight at a
desk near the window, you are very likely not to notice these
changes. In signal processing terms, the adaptation of the eye
is like a filter that blocks slow changes of brightness and colour.
Three mechanisms of the eye are used in brightness
adaptation. The first is the opening and closing of the iris; this
is a fine adjustment comparable to the way a photographer
reduces the camera aperture to obtain greater depth of field
when there is ample light. The second is a neural process,
transformation of sensory data in the eye–brain system; this
is responsible for the almost immediate adaptation that
occurs in situations where the luminance range is not large.
The third mechanism is the bleaching out and regeneration
of pigment in the photosensitive cells of the retina; with this,
adaptation from dark to light is rapid; the regeneration of
pigment needed for light-to-dark adaptation can take up to an
hour. Combined, the mechanisms give a range of sensitivity
that enables us to see in conditions from starlight to bright
sunlight. Figure 1.18 illustrates this.
The reduced visibility of a task when light from bright
objects in the background falls on the eye is the result of
inappropriate adaptation: in photographic terms, the task
area is underexposed because the background illumination
has reduced the eye’s sensitivity.
There are situations where the brightness adaptation of
users must be controlled. The lighting of roadway tunnels must
provide zones of intermediate brightness as drivers enter and
leave. In a cinema, where users may enter from a daylit street,
the sequence of spaces from the entrance, through the
ticketing area, the foyer and the approach to the auditorium
should be a progression of reducing brightness. The same
strategy may be necessary in an art gallery, where the
illuminance on the pictures displayed has to be low to minimise
radiation damage. The visitor is taken through a sequence of
spaces where the brightness of the displays gradually
diminishes and users’ vision becomes increasingly sensitive.
There are two requirements of spaces entered by people
adapted to a higher illuminance. The first is to ensure that
the light falling on their eyes is minimised, so their visual
sensitivity is enhanced; the second is that essential objects
are sufficiently bright to be well visible. These requirements
do not necessarily conflict: the illuminance on the eye from
a source depends on its luminance and its angular size. So
the aim is to provide small areas of relatively high luminance
that enable users to find their way, gain information and
appreciate the displays. The same applies to emergency
lighting that enables escape when the normal lighting fails.
At very low lighting levels, colour can be used selectively.
1.18
Adaptation to low levels of brightness. Subjects sit in a dark room after being
adapted to strong light. At intervals, they are shown short flashes of light
of different luminance. The graph shows the lowest luminance they detect
plotted against the time they have spent in darkness. The angle in the curve
indicates transition between the photoreceptors active at daytime levels of
light (cones) to the more sensitive cells of the retina active at low levels (rods).
Based on work by Arden [51].](https://image.slidesharecdn.com/5681580-250526183703-e4460715/85/Daylighting-Architecture-And-Lighting-Design-1st-Edition-Peter-Tregenza-37-320.jpg)
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- 6. Daylighting The focus of daylighting design is the comfort and happiness of users. People respond in many ways to light, and experience it in terms of what is recognised and felt, not as photometric values. So good design is subtle and many-faceted. It is a concern for the human body’s dependence on daylight, for what gives joy and interest, for the creation of ‘place’, for a building’s effect on its surroundings. A focus on people is essential to the creation of buildings which are sustainable within the natural world. This authoritative and multi-disciplinary book provides architects, lighting specialists, and anyone else working daylight into design, with all the tools needed to incorporate this most fundamental element of architecture. The book is centred on practical daylighting design. It describes how new thinking about peoples’ needs and about the requirements of sustainability is leading to a radical shift in daylighting design practice. It includes: An overview of current practice of daylighting in architecture and urban planning • A review of recent research on daylighting and what this means to the practitioner • A global vision of architectural lighting which is linked to the climates of the world and which integrates view, sunlight, diffuse • skylight and electric lighting Up-to-date tools for design in practice • Delivery of information in a variety of ways for interdisciplinary readers: graphics, mathematics, text, photographs and in-depth • illustrations A clear structure: eleven chapters covering different aspects of lighting, a set of worksheets giving step-by-step examples of • calculations and design procedures for use in practice, and a collection of algorithms and equations for reference by specialists and software designers Daylighting: Architecture and Lighting Design is a book which should trigger creative thought. It recognizes that good lighting design needs both knowledge and imagination. Peter Tregenza is Emeritus Professor in the School of Architecture at the University of Sheffield. As an architect and engineer he has been fascinated by the beauty and complexity of daylight for more than forty years, teaching and studying the subject internationally. He has been Visiting Professor at the National University of Singapore and at the Chinese University of Hong Kong, and has worked in schools of architecture in the UK, North and South America, Australia and New Zealand, and China. He has been involved in the research activities of the Commission International de l’Eclairage, especially the CIE/WMO International Daylight Measurement Project and European Union programmes. His publications include many research papers on daylighting and he is the co-author with David Loe of The Design of Lighting (Routledge, 1998). Michael Wilson is Principal Research Fellow in the School of Architecture and Built Environment at the University of Westmin- ster, UK. He was Director of the Low Energy Architecture Research Unit from 1987 until 2010. He has undertaken more than 25 research, dissemination and demonstration projects in daylighting, acoustics and energy for the European Commission. In particular he coordinated a research project on sun tracking systems and projects producing interactive teaching packages on daylight. He has lectured in the UK, throughout Europe, in South America and South Africa.
- 8. Daylighting Architecture and lighting design Peter Tregenza and Michael Wilson
- 9. First published 2011 by Routledge 2 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN Simultaneously published in the USA and Canada by Routledge 270 Madison Avenue, New York, NY 10016 Routledge is an imprint of the Taylor & Francis Group, an informa business © 2011 Peter Tregenza and Michael Wilson The right of Peter Tregenza and Michael Wilson to be identified as authors of this work has been asserted by them in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1988. Typeset in Univers by Glyph International Printed and bound in Great Britain by Bell & Bain Ltd, Glasgow All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data Tregenza, Peter. Daylighting : architecture and lighting design / Peter Tregenza and Michael Wilson. p. cm. Includes bibliographical references and index. 1. Daylighting. 2. Architectural design. 3. Light in architecture. I. Wilson, Michael (Michael Peter), 1949- II. Title. NA2794.T74 2011 729'.28–dc22 2010028616 ISBN 978-0-419-25700-4
- 10. Contents Acknowledgements viii How to use this book 1 Chapter 1. Criteria of good daylighting 3 The essentials 3 Physical measures and what we see 4 Health 1: the need for regular exposure to daylight 5 Health 2: the need for a view 9 The creation of place 10 Work and comfort 19 Display 26 Chapter 2. What light does 31 Luminous energy 32 Light in the atmosphere 33 Light on a surface and Lambert’s law 35 Large sources, small sources and ideal sources 37 An infinite plane of light and the concept of luminance 39 Parallel beams 41 Surfaces and the nature of reflection 44 An infinity of reflections 47 The daylit room 50 A summary 56 A homily 57
- 11. VI C O N T E N T S Chapter 3. The daylight climate 59 The luminous atmosphere 60 The geometry of sunlight 62 Daylight availability 65 Luminance distribution of the sky 71 The whole climate 74 Chapter 4. Daylight and the form of buildings 77 Climate, environment and structure 77 Sunlight 1: shading and shape 80 Sunlight 2: sunshades and solar collectors 83 Sunlight 3: using reflected sunlight to illuminate rooms 86 Light from the diffuse sky 91 Electric lighting during daytime 93 The view to outside 98 Maintenance 99 Imagination 101 Chapter 5. Energy and control 111 Daylight and energy 111 Control systems 113 Calculating energy use 116 Closed loop control algorithms 117 Chapter 6. Standards, design guidance and development control 119 What standards must do 119 Evidence and judgement 120 A spectrum of design guidance 121 Daylight criteria 1: minimum acceptable conditions in dwellings 122 Daylight criteria 2: minimum acceptable conditions for desk-based workspaces 123 Daylight standards in urban planning 124 Conclusions 130 Discussion 130 Chapter 7. Daylight factors 133 The average daylight factor 134 Correlations and variations 139
- 12. C O N T E N T S V I I Atria, arcades and greenhouses 142 Daylight at a point 146 The horizon factor 147 Chapter 8. Daylight illuminance 151 Illuminance and daylight factors 152 Illuminance from reflected sunlight 154 Skylight and sunlight in the urban canyon 156 Trees, distant surfaces and shiny façades 160 The accuracy of lighting measurements and calculations 163 Chapter 9. Collecting daylight: windows, light pipes and other devices 171 Transmittance 172 Estimating transmittance 173 Glass and glazing 175 Light pipes 176 Light shelves 178 Heliostats 179 Chapter 10. Daylight coefficients and numerical models 181 The fundamental equation 181 Subdivision of the sky 182 Calculating daylight coefficients: finite area methods 184 Samples of rays: the Monte Carlo method 187 An outline of a program 188 The use of daylight coefficients 190 Daylight coefficients and dot diagrams 192 Finally … 192 Chapter 11. Notes and references 193 Further reading: general books 193 General notes 194 Illustrations 195 Chapter notes 195 References 198 Worksheets 205 Algorithms and Equations 249 Index 289
- 13. We are grateful to many for their help in producing this book. Firstly, there are academic colleagues from whom over many years we have learnt much about lighting; we would especially like to thank Professor John Page and Professor Steve Sharples at the University of Sheffield, Professor Edward Ng at the Chinese University of Hong Kong, former colleagues in LEARN at London Metropolitan University, Axel Jacobs, John Solomon, Livio Venturi, Dr Marc Zanchetta, Dr Luisa Brotas and Professor Fergus Nicol, Dr Aris Tsangrassoulis from the University of Thessaly, Professor Mick Hutchins from Sonnergy, Wilfried Pohl from Bartenbach Lichtlabor, and Tony Corlett for help with the graphics. Next, our thanks go to friends in the Society of Light and Lighting, in the CIBSE Daylight Group, in CIE committees and in other international research groups; their enthusiasm and scholar- ship has continually renewed our fascination with daylight. We acknowledge, too, the debt we owe to those who have worked with us as research students: the stimulus of sharing knowledge with challenging and lively minds has been invaluable. We would like to thank the editorial and production staff at Taylor & Francis: they have been encouraging, supportive and tolerant – the qualities that authors most need in a publisher. We are grateful to those who read and commented on various parts of this book during its writing, bringing errors and omissions to our notice. The mistakes that remain are entirely our fault. We know they must exist: we just don’t know where they are. Please let us know of any that you find. Acknowledgements
- 14. 1 This book is about natural light and its use in buildings. It covers sunlight and diffuse skylight; it also discusses the design of electric lighting, because often the most sustainable scheme employs natural and electric lighting together through the day. It relates daylight to climate, and thus to buildings that are sustainable because their design is linked to the natural world of their site. The book has two aims. The first is to give an overall view that includes some of the innovative ideas in daylighting that have arisen during the last few years. The second aim is to provide both the practitioner and the researcher with some up-to-date tools. Daylighting is a subject that crosses professional boundaries and academic disciplines. It features in books on architecture, urban design, environmental physics and psychology. You might have a professional interest in the topic if you are involved in property law or in health care. If you are a researcher, your background might lie in atmospheric physics, social science, engineering or any of several other disciplines. Unfortunately, a common interest does not imply a common approach. What you need to know about daylighting depends on your background and your purpose. So does the form in which you can most comfortably assimilate it: are you happiest working graphically? Or with reasoned writing? Or with mathematics? We have tried to organise the book in a way that makes it accessible to readers from different disciplines, and to be useful at different technical levels. We have also attempted to balance a readable introduction to the subject with a structure that provides a convenient source of reference. There are three elements of the book: The central text 1 . Ten chapters introduce the main ideas. They are in a sequence that runs broadly from design to research – starting with the aims and criteria of lighting design; then looking at the behaviour of light, and concepts of climate and sustainability; then at physical aspects of windows; and finally at theoretical models of daylighting. The topics within each chapter are written so that you can read into them as far as you need and skip the unnecessary. Chapter 11, Notes and references, comments on the main text, gives the sources of material in the book and shows where additional information can be found. Worksheets 2 . These are stand-alone documents aimed at the everyday needs of the designer. They summarise key ideas from the main text and describe, step by step, how to analyse the daylight at a site, how to predict how a building or a lighting scheme will perform, and how to assess the quality of lighting in existing buildings. They include data sheets giving information needed in calculations, and graphic tools. Algorithms and equations 3 . Intended for the researcher or the software developer, this is a list of formulae needed to construct numerical models of daylighting. It treats natural light as a series of transformations of the solar beam, from molecular scattering in the upper atmosphere to the compound interreflection within a room. This section begins with a list of symbols and ends with a list of sources. You will find two themes running through the book. The first is the essential variability of daylight. Every place on How to use this book
- 15. 2 D A Y L I G H T I N G earth has its own visual climate. Daylight varies with season, with global position, and with landmass and ocean. In the tropics, night and day are almost equal and vary little between June and December, while in arctic regions, a 24-hour summer day balances a 24-hour winter night. In cloudless arid regions, the pattern of sky brightness changes only gradually with time and place, while in cloudy regions, the variation can be rapid and chaotic. But this spatial and temporal changeability is not a disadvantage. Quite the contrary: it is fundamental to life. It governs the seasonal growth of plants and animals and their diurnal behaviour. It affects the forms they adopt, their materials and colouring. It affects us humans: physiologically – often without our awareness – and in our cognitive and emotional behaviour. We can infer, from the changing daylight around us in a room, whether we are in a city or the country, in a tropical climate or a temperate one, what the weather is now, what time of day it is, what human activity there is outside. The variability of daylight is not random, and the information that it carries is as important for us as its energy. The second theme of the book is the centrality of people to lighting design. Daylighting is an essential part of sustainable architecture, and design for good daylight can generate architecture that is unique to place and function. But sustainability depends not only on the building being appropriate to the climate: it is also essential that the people who use the building are satisfied with it. The focus of daylighting design is the comfort and happiness of users, and this implies the creation of buildings that are part of the natural world. People respond in many ways to light, and experience it in terms of what is recognised and felt, not as photometric values. So good design is subtle and many-faceted. It is a concern for the human body’s dependence on daylight, for what gives joy and interest, for the creation of ‘place’, for a building’s effect on its surroundings. This is essentially a technical book, but we hope that it might trigger your creative imagination as well as providing knowledge, because both are needed in design and in research.
- 16. 3 one Criteria of good daylighting The human body evolved in the diurnal cycle of light and dark, and is tuned to the spectrum of the sun’s radiation. We respond to daylight in many ways: our luminous environment affects our health; it triggers responses in us that can be traced to require- ments for safety and survival; it affects our interaction with other people; it determines the ease with which we carry out visual tasks. Crucial to all of these is that daylight is not a constant flow of light but something dynamic, varying with time and place. The essentials This chapter, and everything about daylighting design in the rest of the book, could be reduced to three rules: Make the building appropriate to the climate. • Preserve the natural variation of daylight. • Give users control of their own environment. • 1.1 Light carries meaning. A child’s perception of the world of brightness and colour is linked with the growth of language and conceptualisation.
- 17. 4 D A Y L I G H T I N G These are central to the aim of satisfying the users of the building and to the aim of sustainable architecture. The reasoning for them is developed gradually through the book. Physical measures and what we see These are complaints recorded during surveys of buildings in use: ‘The room is gloomy.’ • ‘The whole character of the place is wrong.’ • ‘There’s a shiny reflection in my computer screen.’ • ‘The sunlight is dazzling.’ • ‘I can’t control the blinds and I can’t open a window.’ • ‘It’s OK if you sit by the windows but too dark at the back • of the room.’ ‘The electric lights are on all day even though there is • plenty of daylight.’ ‘I can’t see out of the window.’ • ‘It’s too exposed, not enough privacy.’ • ‘There is so much light that my curtains are fading.’ • ‘The new building opposite is reducing my daylight.’ • There are as many criteria of good lighting as there are ways in which a design can fail. These complaints are typical, and each points to some factor that the designer has to consider. Their implications extend across the whole scale of building design, from the orientation and block planning of the site to interior detail. The first conclusion to be drawn is that the aim of lighting design goes far beyond the mere provision of some given quantity of illumination. The essential variability of daylight Natural light is always changing. It varies in time, sometimes smoothly and slowly, sometimes rapidly and chaotically. It varies spatially at many scales from the differing daylight climates across the globe to the complex and subtle distribution of brightness at the scale of an individual room. If you are in a daylit room now, look around you. Can you tell where light has been reflected by the ground outside? Where it has come directly from the sky? Where a patch of brightness is due to reflected sunlight? Look at Figure 1.2. What can you deduce about other windows in the room?1 Any daylit room at any moment is unique. Its pattern of brightness depends on where it is in the world, and on the time of year and time of day. Variability in space and time is the dominating characteristic of natural light. For much of 1 It’s a subtle effect, but if you look at the white panel below the window, you realise that there must be another source of light in the room. There are, in fact, windows in the opposite wall. 1.2 Design for a cloudy climate: an eighteenth-century window giving the interior of the room the view of a large angle of sky. The Library, Stevenstone, Devon, UK.
- 18. C R I T E R I A O F G O O D D A Y L I G H T I N G 5 the twentieth century, this variability, especially its apparent randomness in cloudy regions, was seen as a serious drawback. In offices, classrooms and most other types of interior, uniformity of illumination was taken to be an essential characteristic of good lighting. But people like daylight. Most prefer to live and work in daylit rooms. If some activity requires a windowless space, there is an urge to take a regular break, to ‘get some daylight and fresh air’. There has not been enough research to be certain why we have this desire for daylight. Strong but circumstantial evidence implies that changeability is crucial: the continual variation of brightness in a daylight room is, literally, stimulating because our senses respond to change, not to unvarying conditions. It is not changeability in itself that matters: natural light, by its spatial and temporal variability, carries information, and this information is at least as important to us as the energy of the radiation. For people in a building, the light that flows in through windows is worth much more than its value simply as radiant energy. It tells about the world outside, and it is natural to us because our bodies evolved in the swing of night and day, summer and winter. There is a fundamental difference between an objective description of light and what we perceive. The daylight flowing into a room can be described physically in several ways: as luminous flux; as a luminance distribution; as radiant energy that varies in spectrum, time and direction. Subjectively, we could visualise it as a mere pattern of brightness, but this is not normal perception: looking outside, we see a view; and inside we see walls, ceiling and floor, and all the things and people they enclose. But exactly what we perceive, and what it means to us, depends on our individual experiences and expectations: no two people ‘see’ the same room. Moreover, the perceived environment is not dependent on visual stimuli alone: it is influenced by other physical factors, such as noise and heat, and it is affected by the social environment. Our awareness is of a place as a whole, and our reactions to it are influenced by our frame of mind, our motivation and our interest in whatever we are doing. Lighting affects mood: but the mood it creates depends on us. The sunlight of an early spring morning can lift the spirits and give a new enthusiasm for the tasks of the day; or have an opposite effect if we fear what the day may bring. Standards and reality Daylight varies in a complex and not wholly predictable way; so does human response to daylight. But design criteria, the standards and guidance required in practice, must be objective and simple, consistent and replicable. It must be possible to test whether or not a lighting situation reaches stated criteria or to calculate whether a design, when built, would do so; and both measurements and calculations should be easy and robust. This is discussed more fully in Chapter 6, and the conclusion reached is this: meeting the requirements of published standards, no matter how assiduously they are followed or how extensive the criteria, does not necessarily produce good lighting. Well-conceived standards give points of support in the process of designing but they are no substitute for the designer’s understanding of the needs and wishes of the people who will live or work or play in the building being created. Health 1: the need for regular exposure to daylight Electromagnetic radiation affects the body, both harmfully and beneficially. We evolved in the environment of light from the sun, and we require it for the maintenance of health. But exposure must be controlled: excessive short-wavelength radiation – x-rays and beyond – causes deep-tissue damage; radiation at wavelengths near the visual range can damage the skin and the eyes. The harmful effects can be both rapid (such as burning) and long-term (such as stimulation of cancer growth). Direct sunlight on the body can be valuable, but there must be a balance between the risks of over-exposure to sunlight and under-exposure. The design of a building cannot by itself ensure the optimum exposure to daylight for maintenance of mental and physical health: the way a person lives and, in the case of residential buildings, the management regime of the institution are crucial factors, but a poor building can have a seriously detrimental effect. The fundamental needs are: A 24-hour cycle of illumination that includes periods of 1 darkness and of bright light Exposure to bright daylight during winter months 2
- 19. 6 D A Y L I G H T I N G The need of building users for a sense of contact with the 3 outside world Avoidance of glare that causes discomfort or reduces 4 visibility of hazards The importance of each of these depends on the building type and the circumstances of the users. The influence of the built environment on health is greatest for those who are confined – the old and the sick, those in prison, those whose work keeps them indoors through the hours of daylight. Circadian rhythms, SAD and the need for light The natural 24-hour cycle of light and dark is used by the body to regulate the daily sequence of physiological changes – of sleep, hunger, body temperature, alertness, and of almost all hormone production. Circadian rhythms are ‘clocks’ in the bodies of mammals and many other organisms that control these changes. Disrupting them gives the symptoms of jet-lag and shift-work, and of sleep disorders. There may be long-term consequences: for instance, confinement in windowless cells may contribute to mental health disorders in prisons. Our various circadian rhythms are interlinked and together have an inherent cycle time of slightly more than 24 hours; but, crucially, they are modified by external stimuli, and exposure to light is probably the most important of these. In the retina, there are photoreceptors other than those used for vision, and these trigger hormonal changes associated with the day–night cycle. The effect of light on the hormonal changes increases with illuminance but values as low as 100 lx on the eye have a measurable effect. The spectral sensitivity to radiation of the non-visual retinal receptors differs slightly from that of the rods and cones (which define ‘light’), the peak sensitivity occurring at the wavelengths where we see blue–green. Periods of darkness are as necessary as exposure to bright light, and in a healthy state the light–dark cycle is synchro- nised with the person’s diurnal activity–sleep cycle. With older people, especial care must be taken to ensure sufficient illumination, because the transparent parts of the eye become yellowed with age and thus reduce the blue–green disproportionally. There are categories of people with a higher than average probability of suffering from deprivation of light or from conditions associated with disturbed circadian cycles. They include shift workers; people who are disabled by advanced age or other chronic conditions and are unable to go outside; people confined within an institutional building where there is continuous lighting for care or for security; and people who frequently make long-haul flights. There is substantial research evidence that, with people of all ages, good sleep and associated improvements in behaviour are associated with therapeutic exposure to bright daylight within a 24-hour light–dark cycle. Seasonal affective disorder (SAD) is a depressive illness that varies with the time of year. It can occur during winter, with symptoms common to other types of mental depression such as oversleeping, mood changes, lack of energy and over-eating; there is also a summer form in which the symptoms tend to be the opposite – lack of sleep, loss of appetite, weight loss. The winter form is the more usual and is found mainly in young adults, but it also affects older people, and women more than men. The mechanism of the winter disease is clearly related to exposure to light: the symptoms are relieved when the sufferer receives daily exposure to a bright source of light, they disappear with the onset of summer and recur in autumn, and they are found predominantly in people living at latitudes distant from the equator. The summer form of SAD is much rarer and is not necessarily a response to high levels of light; it may be due to other factors such as overheating or behavioural changes during hot summer months. Although the type of daylight climate in which SAD tends to occur is known, further research is required about the regime of illuminances that triggers the disease. The evidence available suggests that the risk of SAD becomes significant where people live in an environment in which illuminance on the eye is below 1 klx for much of the day. Therapeutic doses are better understood: when daily exposure to bright light is used clinically as an antidepressive, typically the patient spends 30 minutes every morning facing a ‘light box’ – fluorescent lamps mounted behind a diffusing screen – which produces 10 klx at the patient’s eyes. A lower level of light, 2.5 klx, may be used for a period of 1–2 hours. The total dosage required, the product of illuminance and time, tends thus to be about 5 klx h. Radiation towards and beyond
- 20. C R I T E R I A O F G O O D D A Y L I G H T I N G 7 the blue end of the visible spectrum is more effective than longer wavelengths. It is found also that the light treatment for SAD patients is more effective during the morning than the afternoon, and the normal recommendation is for exposure to light immediately after waking. Figure 1.3 shows how typical winter values of illuminance outdoors vary with latitude; they give mean daylight levels not for the shortest day of the year but a month later, 21 January, which is more representative of the winter period as a whole. The horizontal axes of the graphs extend from 20°, just within the tropics, to 60°, close to the Arctic Circle. Figure 1.3(a) shows illuminance on a vertical surface and is approximately the illuminance on the eyes. The two upper curves give values at 9 am and mid-day when the sun is shining and the receiving surface is orientated to face the sun; the two lower curves show the average illuminance on the surface when the sun is obscured. Figure 1.3(b) gives the time of sunrise on 21 January. It can be seen that at latitudes of 50° and above, not only are the hours of daylight short but, outdoors in cloudy weather, the mean diffuse illuminance on the eye barely exceeds the levels needed for SAD therapy. Indoors on an overcast day, an exposure to light equivalent to a therapeutic dose could be received only by a person remaining close to a window for several hours. When the sun shines in through a window, however, there is ample light. It is probably not just for its warmth that sunlight is welcomed in cold weather: its high brightness may stimulate a real uplifting of mood in those affected by winter depression. The conclusion to be drawn is that in cool climates the conditions that engender SAD are likely to be experienced by anyone who is confined indoors. This applies to a significant proportion of the population and to several building types, but is a particular important consideration for people in care buildings. It has been found, for instance, that dementia patients, and older people in residential homes generally, tend to have significantly less exposure to environmental daylight than other people living in the district. Sunlight, synthesis of vitamin D and other health factors A deficiency of vitamin D is associated with rickets and poor bone growth generally; among older people, it may hasten skeletal frailty and thus an increased risk of fractures. Exposure to sunlight is the natural means by which the body produces vitamin D. Overexposure to sunlight causes skin damage that leads ultimately to cancer. Different groups of the population, by their styles of living, have opposite risks to health: the young and the rich from excessive exposure to the sun, the old and the poor from inadequate exposure. Conclusions for design Buildings in which the occupants are confined during the 1 hours of daylight, such as residential care homes, prisons, hospitals and factories with shift working, should have freely accessible internal areas with strong daylight. In cool climates, these areas should receive direct sunlight, but there should be blinds or other means of control. The daylit areas should be useable for normal daytime activities. Intermediate indoor–outdoor spaces such as conservatories satisfy these requirements. Bedrooms and dormitories generally, and places such as 2 hospital wards where residents regularly sleep, should have very low levels of light during the normal sleeping 1.3 Winter daylight: January 21 in the Northern Hemisphere. (a) Average illuminance on a vertical surface outdoors at 9am and noon, facing the sun and on a cloudy day. (b) Time of sunrise (in solar time).
- 21. 8 D A Y L I G H T I N G 1.4 What we like to look at. A general view containing elements that are preferred: natural things – trees, grass, water; some activity; a range from nearby ground to distant objects and sky. King’s Park, Perth, Western Australia 1.5 The type of view that is not preferred: built, not natural, objects; a short distance range, no sky. But usually a room looking onto this would be preferred to a windowless interior, and if the viewer had a personal interest in the place, or if there were security needs, such a view might be considered essential.
- 22. C R I T E R I A O F G O O D D A Y L I G H T I N G 9 periods of residents or patients. Curtains or blinds should exclude unwanted light from outdoors; this includes stray beams from exterior night-time lighting, and daylight of the early morning and late evening in high-latitude places. Where needs of safety or security require illumination for supervision, this should be screened from the view of those sleeping; controls such as movement detectors should be used to allow near-darkness wherever possible. Many people, particularly the elderly, wake from time to time at night; local lighting should always be provided, controllable from the bedside. Health 2: the need for a view This is a topic where recent research has greatly altered thinking. Until recently, standards and daylighting codes have tended to treat a window has having two visual functions: ‘view’, what you see looking outwards, and ‘daylight’, the illumination that is coming in. But this distinction is misleading: it is the daylight that carries the view. Or, putting this more precisely, the perception of a view is one of the ways in which the body responds to daylight. When we look outwards through a window, daylight reaches the eyes from many angles. Some of the incident light is direct from the sky, maybe the sun itself, some is reflected by exterior surfaces such as the ground and other buildings. This field of light varies in intensity and colour with direction. The miracle of vision is that we can use this complexity to construct an image of the world before us. Some rooms must be windowless: auditoria, film and television studios, art galleries displaying light-sensitive materials – in general, places where illumination must be controlled at low levels. But a windowless room is strongly disliked if there is no obvious reason why daylight should be excluded. Any view is better than none: if the only window in a basement flat looks out onto a brick wall, most people would far prefer that to a windowless interior. Even if the user keeps blinds or curtains always closed, the existence of a link with the outside is valued. An attractive or interesting view can have a therapeutic effect. In particular, windows with views onto nature can enhance working and well-being. It was found, for example, that patients recovering from surgery in a ward with windows overlooking trees required less powerful analgesic drugs and had shorter recovery times than matched groups of patients in a ward with a view only of a brick wall. Similarly, the glare discomfort caused by a bright sky or by sunlight reflected from light-coloured surfaces is lower when there is an 1.6 This window controls sunlight penetration in a warm dry climate, while allowing air movement; it prevents an inward view (because the interior is dark compared with the surface of the lattice screen) but enables people inside to see outwards. Iran
- 23. 10 D A Y L I G H T I N G interesting natural view than when the view is of an urban scene of the same brightness. A substantial amount of research has been done on people’s preferences for the content of views. In a typical experiment, subjects sit in a simulated room; images are projected onto screens seen through window-like openings and the subjects are asked to rank these. The following results have been found by several investigators: Views that encompass a wide scale of distance are 1 preferred to those of limited extent; the scenes ranked highest encompass some sky, distant landscape, a middle distance with movement or activities, and objects and the ground nearby. Views of natural scenes are preferred to those of urban 2 environment; scenes containing water are especially popular. When a person is confined indoors, in buildings such as 3 a care home, windows that overlook everyday activities in the community can provide some compensation for restricted social contact. There are, however, two factors that override these preferences: security and privacy. The need for security normally implies a need to maintain awareness of specific external spaces: examples are supervision of children playing, awareness of people approaching the entrance, a general observation of the site to deter intruders. These activities constitute visual tasks and should be treated as such. The views they give do not necessarily meet the need for contact with the outside world. The converse of a view out is privacy, the ability to prevent other people seeing in. This requirement is highly dependent on culture and it can take precedence over a view out. In most cultures, people in their home will close curtains or blinds if passers-by could invade privacy, even if this sacrifices a valued view. They would be dissatisfied, however, if the room were windowless. The provision of an outward view and control over any inward view depend both on a building’s site layout and block form, and on the fine detail of window design. Traditional architecture exhibits many solutions to the apparent conflict between criteria of inward and outward view; some are of great ingenuity and beauty, particularly in countries of the Middle East. It is not just the direct view outwards that is valued. Daylight brings information even if a direct view is blocked. The continuously varying illumination from a window gives awareness of the outside world even when there is no direct view. From the changing pattern of brightness within the room, we know whether it is sunny outdoors or overcast and raining, whether it is windy with a rapidly changing sky or is settled and calm; we sense also the time of day; and often in an urban building we are aware of reflections or moving shadows of road traffic. Conclusions for design Unless the function of the room is incompatible with 1 daylighting, or it is used only for short periods, every workplace and every habitable room in a dwelling should have a view through a window to the outside. If a workplace must necessarily be a windowless room, workers should have free access to a nearby space with a good exterior view. A view into another internal space is less liked than an external view; and, if there can be only an internal view, this should be into a large daylit space, such as an atrium. In hospitals, residential care buildings and other buildings 2 where people are unable to move around freely, interesting views, particularly of natural scenes, should be visible to users from their normal daytime positions. The variation of daylight on the walls and ceiling of a 3 room should not be masked by electric lighting. If this is necessary to enhance task illumination or to brighten surfaces that receive little daylight, users should still be aware of the natural changeability of daylight. The creation of place A ‘place’ is somewhere with meaning, somewhere that arouses associations, that can trigger memories of earlier occasions, that can stimulate emotions. In the greatest buildings and urban spaces, we find an inexhaustible richness of associations. Indeed, the possession of such richness could be the defining characteristic of great work in any art. But every building, anywhere in any town, can arouse thoughts and feelings, and this is an inevitable outcome of the processes by which we perceive the world. The experience of a place can be profound and it can be fleeting, but it is rarely neutral.
- 24. C R I T E R I A O F G O O D D A Y L I G H T I N G 11 Architectural design is the creation of place. So, therefore, is the choosing of brightness and colour, because these are elements of architecture. The lighting and materials of a room, the distribution of light and dark, of chroma and texture, not only determine the physical visibility of things, but they establish the nature of the place, its character, its meaning. Whether or not the designer intends it, the room (or the building or the urban space) that is created will be associated in the mind of every user with places that he or she has previously experienced. To see why this is so, and to understand the implications for people’s expectations and satisfaction, we must make a brief review of perceptual theory. Images and words Look at the photograph in Figure 1.7. Suppose you were instructed to study this for one minute and then, half an hour later, sketch it from memory: could you do it? Almost certainly. The appearance of the sketch would depend on your drawing skill, but it is very likely that you could reproduce the picture in a recognisable way. And if you could draw the place, you could also describe it in words: ‘It is a bedroom with two single beds with white bedspreads. It is daytime and there is a large square window …’, and so on. Consider an alternative. Suppose you were instructed to subdivide the picture into a grid of 1000 small squares and then, starting at the top left-hand corner, remember the brightness and colour in each square. This would be impossible – unless you had some method of reducing all these values to some pattern or formula. The result of our perceptual process is not like a bit-mapped digital image from camera or scanner. We do not see an array of millions of luminous points: we recognise a ‘room’, a ‘window’, a ‘chair’. Patterns of light and colour have meaning, and the ‘meaning’ is an outcome of the method used by the eye and brain to organise and remember a colossal quantity of information. Perception is, in essence, the process of linking immediate sensory information with remembered experience. The distribution of brightness and colour that constitutes our visual environment is never treated as an abstract, meaningless pattern. For safety, for survival, we have always needed to identify things that might benefit or harm us. The result is that our awareness of a place goes beyond mere recognition: what we see governs our expectations and our satisfaction, it affects our mood, our confidence, our approach to our activities there, and how we react with other people. It is no accident that we can describe in words what we can draw. In developmental theory, a schema (plural schemata) is an organised set of memories that builds up though repeated experience. As we pass through different stages of childhood, schemata develop as we gain language: we learn that a ‘chair’ differs from a ‘table’ when we understand what ‘sit’ means. By experience, we begin to recognise the typical shape and dimensions of a chair; and when surprised by exceptions, we construct more complex schemata with the ability to recognise differing categories, 1.7 Could you look at this photograph for a minute then draw it from memory? Aalto House, Munkkiniemi, Helsinki
- 25. 12 D A Y L I G H T I N G such as ‘armchair’, ‘car seat’, ‘throne’. Schemata link sensory memories with words and concepts. Culture and climate A ‘culture’ could be defined as a commonality of experience, a sharing of memories. Because perception is the process of relating what is immediately sensed to concepts derived from earlier experience, people with similar cultural backgrounds make similar associations between words, images and emotions. That is why a story-teller can trigger common emotions in a group of listeners, or why it is possible to use lighting to change a stage set of meaningless blocks into a scene that consistently conveys the nature of a play. The converse is that people from dissimilar cultures ‘see’ quite different places. How would you describe the scene shown in Figure 1.8? Is it ‘homely’? Or a place you recognise as a traditional English cottage but quite different from your own home? Or somewhere so foreign that you feel slightly threatened? There are cultural differences due to different climatic experiences, and these affect expectations about comfort and discomfort. If, for example, a group of students of various nationalities is asked to write down their reaction to a picture of a dark room with small windows, those who come from a hot dry climate tend to say that the room looks pleasantly cool; those from a northern temperate climate tend to describe the room as gloomy. Cognitive awareness of our personal environment can range from entirely subconscious to intolerably distracting: what determines this is, firstly, the extent to which the place is consistent with our schema, and, secondly, the extent to which we concentrate on some other topic. These interact: if what we are doing or thinking is important and the environment is unsettling, our performance or pleasure is diminished. In a familiar situation, where all that we subconsciously sense is what we expect, we are likely not to notice the surroundings. If something is incongruous, or if we realise what sort of place it is but it is not our normal setting, we are 1.8 How would you describe this scene? What feelings does it arouse in you?
- 26. C R I T E R I A O F G O O D D A Y L I G H T I N G 13 aware of this. If every clue to recognition implies something different, we are confused. What we consciously remember from a scene, or what we include when asked later to describe it, varies between us as individuals, not only in ‘subjective’ judgements of mood or preference but also in ‘objective’ tasks such as estimating the size of one element in relation to another or discriminating between objects that differ only slightly. Both preference and task performance can be shown to vary systematically with characteristics of the individual and also with common characteristics that define a particular culture. There are also many results that imply that satisfaction with any particular circumstances depends on expectation. We are happy if we get more than we anticipated and dissatisfied if we get less, but the level of our expectation depends both on the immedi- ate context and on all our earlier experience. Assumptions and constancy When we have insufficient evidence to recognise unambiguously a place or an element in a scene, we make assumptions – consciously and subconsciously – about both the social context and the physical. We do this continually in our perception of the three-dimensional environ- ment. For instance, a daylit wall varies greatly in luminance, but we perceive this as a change of illumination rather than a variation in surface reflectance, because that is what experience tells us is probable. Look at Figure 1.9: what our eyes focus on is just a pattern of coloured inks on paper. But the distribution of brightness and colour of this pattern is like many we have experienced before; so we ‘see’, that is construct in our mind, the image of a three-dimensional object. What is more, we recognise it as a carved figure in a museum, a representation of a middle-aged man dressed in historical clothing. We would even be willing to attribute a mood and character to him. The phenomenon of ‘constancy’ is the result in perception of assuming that one physical characteristic rather than another is varying. We take the most familiar explanation when there is ambiguity: coloured lighting falling on a person’s face is recognised as that rather than as sudden colour changes in the skin. The ability to separate the effect of illumination from surface characteristics and deduce that it is the light that changes is ‘lightness constancy’. It depends on our experience of similar physical situations and on the availability of clues to resolution of ambiguity. But constancy can break down. If false clues invoke the wrong assumptions, we see ‘illusions’. This can occur with familiar visual tricks like Figure 1.10, where an implication of a converging perspective makes the horizontal bars seem unequal. Constancy often breaks down when a source of light is hidden: a picture illuminated by a masked spotlight to a much higher brightness than its surroundings can look like a transparency lit from behind. And, in Figure 1.11, the church seems to be brightly painted, but the façade is grey stone and the illusion of a painted surface is the result of projected light. 1.9 You are looking at a two-dimensional printed pattern, but not only do you interpret it as a carved figure, you probably attribute to it emotion and character. Medieval pilgrim, Museo das Peregrinacions, Santiago de Compostela
- 27. 14 D A Y L I G H T I N G The church was photographed from several viewpoints; the images were coloured, detail-by-detail, then projected back on the façade from the original viewpoints. Consistency Perception is a process that integrates all the physical senses, not just the visual; and, crucially, it depends on the social environment. Our response to a place includes expectations both of specific physical characteristics and of the ways in which people would behave in that environment. Words like ‘church’, ‘pub’, ‘school’ invoke visual images and recognition of specific sensory environments: they also invoke behav- ioural memories. We know what a classroom is like and we expect it to differ from the interior of a church or a pub. We behave differently in different types of room and we expect others to do so. We form integrated concepts through repeated experiences: language, sensory awareness and social actions become interlinked. Sound, smell, touch, air movement, air temperature, radiant heat – and the way these alter with time and with our own movements – all of these can affect what we ‘see’. If there is inconsistency – for instance, if a restaurant looks luxurious and expensive but sounds like a fast-food place – we are puzzled or confused. We are more disturbed still if the behaviour of other people is inconsistent with our expectations of the place. The process of place recognition is usually below the level of conscious awareness. It is a search through the schemata formed though previous experience for the one that best fits the present sensory stimuli. A place is identified when we have linked it with a specific schema. It then becomes associated with all the experiences that have accumulated in memory around the selected schemata. These associations then generate expect- ations about the physical and social nature of the place we see. It is enough to imagine a room, or simply use its name, to invoke expectations. A type name, such as ‘bedroom’, implies that the room will have those features that define the type, the clues to recognition: in a bedroom there will be one or more beds; there will be conditions of heat, light and sound that make sleeping possible, and the room will have various other characteristics that distinguish it from, say, a bedroom furniture showroom in a department store. We know also that bedrooms vary greatly, but, because the majority lie within a 1.10 The Ponzo illusion. The converging lines carry an association with increasing distance, so the grey bars, which are identical, appear to be different sizes. 1.11 Projection of coloured lights gives an illusion of a painted façade. Saint Nizier, Lyon
- 28. C R I T E R I A O F G O O D D A Y L I G H T I N G 15 fairly narrow range of size, shape, layout and materials, we could easily describe a typical example. We have an idea of what is typical for many types of space. The ‘normal’ room Let the term ‘normal’ mean a set of expectations about the physical environment, expectations that are evoked by the name of the place – either a generic name, such as ‘bedroom’, or the name of somewhere specific. The test of whether a ‘normal’ place exists in a person’s mind is whether qualifying words can suggest something unusual. The phrase ‘a very big bedroom’ implies one much larger than most of those in our previous experience, and it is meaningless to say ‘a very big bedroom’ unless the hearer not only has a concept of a ‘normal’ bedroom, but has one that is similar to the speaker’s. The fact that we use such expressions prolifically in everyday speech is evidence that, firstly, words such as ‘bedroom’ can conjure a clear image of a place and, secondly, there exist typical images, or sets of expectations, that are common between people. This gives us a huge advantage in communication. It is not necessary to give detailed descriptions of things of shared experience. By triggering recall of memory in the hearer, a few words can, in effect, convey complex informa- tion about places, or people, or pictures. We have a highly developed ability to deduce the culture of other people from the particular words they use, and this influences our social behaviour. The concept of ‘normal’ can be extended beyond particular types of room to the construction and shape of building elements – the slope of tiled roofs, for example, or the proportions of structural columns. If most of the buildings we have seen have similar shapes and dimensions when constructed of particular materials, these become ‘normal’. We comment on exceptions: ‘The roof of that house is very steep’; ‘That column doesn’t look safe!’ The rectilinear daylit room There is a shape that occurs, with subtle climatic modifica- tions, almost everywhere in the world. It is found in vernacular architecture wherever local building materials naturally lead to planar forms (the timber frame, the masonry wall) and internationally with steel and glass, and the boxed shuttering of reinforced concrete. It is found where space needs to be subdivided regularly. The rectilinear room is the most common interior space: it is the living room, the classroom, the office – the kind of room in which most people spend many of their daytime hours and where many of the significant events of life take place. There is convincing evidence that rectilinear room geometry is ‘normal’. An example is the demonstration room invented by the American ophthalmologist and psychologist Adelbert Ames, Jr (1880–1955). It is shown in Figure 1.12, and may be built either as a scale model or full size. In plan and section, it is far from rectangular – the ceiling slopes downwards and opposite walls differ in length – but, when viewed from one position, a peephole in one of the walls, it appears in the perspective of a rectilinear room. The only peculiarity is that, seen from the peephole, people inside the room appear to change size as they walk around. So strong is the association between a rectilinear room and a visual pattern of converging lines that, faced with ambiguity, the brain causes us to perceive a familiar room form occupied by weirdly changing people rather than an unexpected room shape enclosing ordinary men and women. The illusion does not always work: if the viewer has previously seen the room from another position, the distortion is recognised from the viewpoint, or if a person inside the room is well known to the viewer. 1.12 The Ames room, seen from above and (lower drawing) from the viewpoint indicated by the arrow.
- 29. 16 D A Y L I G H T I N G In each case, additional knowledge causes the viewer to adopt an alternative schema. The windows in a ‘normal’ rectilinear room are usually in one wall or two adjacent walls in buildings of domestic scale, for practical reasons of layout planning; larger spaces such as classrooms may have windows in opposite walls. Roof openings are less common than side windows, again for obvious practical reasons. Associated with ‘normal’ room dimensions are, therefore, ‘normal’ patterns of light, the characteristic patterns of daylight distribution. When windows are in one wall only, or in adjacent walls, the pattern of illumi- nation is strongly asymmetrical. There are steep gradients of brightness across the room surfaces, and the relative amounts of light falling on vertical and horizontal surfaces changes with distance from a window. Most importantly, the pattern of surface brightness and the absolute quantity of light in the room are not constant but change with time in a way that is related to the world outside. There is experimental evidence that supports the existence of ‘normal’ brightness distributions. The experiments used test rooms where illuminance on the walls, ceiling and desktop surfaces could be adjusted separately. Subjects were asked to adjust the lighting to their preferences or to select from preset luminance patterns. Those chosen had the characteristics of daylit spaces, even though the rooms were windowless. Subjects tended to prefer working-plane illuminances signifi- cantly greater than the minimum needed for office-type visual tasks; mean wall luminances were moderately high, but exhibited a large difference between maximum and minimum. ‘Visually interesting’ or non-uniform wall luminance patterns were preferred, together with acceptance of temporal varia- tion. An important result from such experiments is that subjects are able to make consistent judgements about the lighting of a room and that they are consistent in the use of words and metaphors to describe particular lighting situations. Daylight quantity Surveys of daylighting preferences among different groups of users have produced widely varying results. Occupants of very high-density residential blocks in Hong Kong were found to be satisfied with much lower levels of daylight than expected in social housing in Western Europe; occupants of expensive modern apartments tend to expect more daylight (and more extensive views out) than those living in low-cost areas. The nature of the architecture is also significant: less light is expected in the cottages of a rural village than in a high-ceilinged Renaissance villa or a modern dwelling. The question ‘How much daylight should be provided for a particular room type?’ implies two further questions: ‘How much do people expect?’ and thus ‘What is “normal” for them?’ There is no universal criterion of daylight quantity. What is found to be satisfactory depends on the function of the building, its architectural nature and the culture of the users. Expectations probably also vary with time: as a population becomes used to a higher standard of housing, for example, or as fashions change, or as matters such as sustainability become widely accepted. An indication of what was ‘normal’ in buildings can be inferred from published guidelines, rules of thumb and mandatory requirements. These go back as far as Vitruvius; they are found in key books on architectural principles by Palladio and other authors in the Italian Renaissance; there are eighteenth and nineteenth century European examples, and there are regulations, standards and byelaws published in many countries during the last 150 years. These do, of course, describe what each author considered to be either minimum requirements or good practice rather than the conditions found in existing buildings of the time. We will take them as indications of what users might have expected in a good building. Most give required window sizes either in terms of the ratio of window area to floor area or in terms of the ratio of window area to inside window wall area. Some recommend specific proportions of windows and maximum room depths in relation to window height. What is remarkable is the consistency of the recommen- dations over many centuries. For the window area : floor area ratio, typical ranges of values are housing 8–13% schools 17–25% At the beginning of the twentieth century, the requirements of the London Building Act were 10% and 20% for the two building types, and these values were echoed in byelaws from other parts of Britain, continental European cities and
- 30. C R I T E R I A O F G O O D D A Y L I G H T I N G 17 cities in the USA. In some places, equivalent regulations exist now. Figures from the first half of the last century must be seen in the context of rudimentary electric lighting and substantial atmospheric pollution from coal burning. Especially, it must be noted that daylighting was the principle method of illumina- tion, and this was why relatively large glazing areas were required in schools and workplaces. Expectations ‘Normal’ characteristics extend beyond particular place types. For example, some assumptions we make from common experience are: Floor and ground surfaces are usually dark-coloured, but • not black; ceilings tend to be much lighter; walls tend to vary greatly because they are broken up by doors, windows, pictures and many other items. The flow of light is usually downwards, from the sky and • from overhead electric lighting. Distant objects outdoors tend to appear weaker in colour • saturation than nearby objects, owing to scattering by the atmosphere. A place that differs from such norms can take a special character. A strongly lit white floor can trigger associations with snow or the sensation of walking on a cloud; an upward flow of light from a window and a bright ceiling suggests sunlight on the ground outside; a dark ceiling can make a room seem cave-like, especially if all the enclosing surfaces are dark-coloured and matt. Stage design uses these common assumptions to create illusion: a face lit from below looks threatening, even diabolical; a gradation from strong colour at the front of the stage towards a uniform pale blue at the horizon makes an illusion of great distance. The two images in Figure 1.13 illustrate the visual significance of the floor reflectance. Expectations and the needs of the user Should a bedroom ‘look like a bedroom‘? Should a building, or a room, or a source of light, draw attention to itself, or is it better that it remain part of an unnoticed background? 1.13 If the floor or ground surface is darkened, the perceived character of the place is changed. Th e interreflected light is reduced, thus reducing the brightness of other surfaces. British Museum, London, original (upper) and modified image (lower)
- 31. 18 D A Y L I G H T I N G There is an important decision that the designer must make: it is whether a place should be ‘normal’; whether, that is, a setting should be accepted subconsciously or should attract attention. A workplace must maintain stimulation but not be distracting; a display must not go unnoticed; a building where people are already overwhelmed with information must not add more. Awareness of our personal environment ranges from the entirely subconscious to the full focus of our attention. We can be so concentrated on a thought or an activity that we entirely miss what is happening around us; or the opposite – we can be so overwhelmed by a place of natural beauty or magnificent architecture that all else is forgotten. Sometimes there is conflict – we try to concentrate on a task but are continually distracted by something we can see. The more ‘normal’ a place, the more likely that it will remain below the level of conscious experience. This is helpful where users are anxious or handicapped, such as unconfident travellers in a large airport terminal or patients in a hospital. A building that by self-display increases the amount of information that users have to assimilate can increase their distress. But complexity and contradiction are elements of architectural composition, and these imply that a place should be noticed for its own sake. A building may provoke thought, and hold the viewer’s attention by saying more than can be revealed at a quick glance. It can contain references to recent events, to cultural memories and to the other arts; but any resulting ambiguity may be worse than confusing to a distressed person. For every place, there is an optimum level of consistency between the different senses, between the physical and the social environments, and between expectations and actuality – the balance between the ‘normal’ and the strange. When tasks demand concentration, the purpose of the building is to provide a comfortable helpful enclosure. Where users have sensory or cognitive disability, or are anxious or distressed, every aspect of the place should aid and guide. Not only must the place be ‘normal’, there must be consistency in every aspect. But where display of the building itself is an objective – where the architecture can be stimulating, exciting, innovative – it is not enough to offer only the ‘normal’. The aim is twofold: to provide sufficient clues to establish recognition of the type, and to present the unexpected. Both are necessary; if a place is so bizarre that it is not recognisable, the degree of innovation is not measurable. Designers and the rest of the world Successful design depends on anticipating users’ expectations about the physical characteristics of the room. This depends on many physical and social factors. Expectations are shared between people of similar background, but vary with climate and culture. They may be different between the people who commission a building and those who will live and work there, because in most cases clients and users are different people. A professional designer does not have the same perception of the visual environment as people untrained in the discipline. A five-year course in architecture, for instance, not only gives the student a technical competence: it creates new attitudes, new visual standards, and a changed meaning to many common words. Above all, we become sensitised to our specialism: a highway lighting engineer is much more aware than other people of glare from street lights; an architect looks more at buildings, and at different features of them. It is essential for the designer to be aware of this and to use language – both the language of speech and the language of the visual world – that carries meaning for the layman. Conclusions for design People have clear expectations about the appearance of a 1 place. These depend on culture and personal experience; they govern how people behave in the place, their motivation to work and their attitude to change. There exist assumptions about the appearance and contents of particular types of building; these can be triggered by the name (‘bedroom’, ‘department store’, ‘church’) and by characteristics that lead to recognition of a particular type of place. A designer’s perception is likely to be different from that 2 of a building’s users. It is important to recognise this, especially when designing for users with disabilities such as dementia or from a different cultural background.
- 32. C R I T E R I A O F G O O D D A Y L I G H T I N G 19 Places may be recognised differently, and behavioural clues misinterpreted. The extent to which a place is consistent with people’s 3 expectations determines whether it is recognised as a particular type of place and whether it is noticed. Where task performance is crucial or where people may be stressed, it is important that the enclosure is not unsettling or distracting. Work and comfort Reading and writing are visual tasks; so are using tools, assembling components and many other activities in a workplace. But there are visual tasks of everyday life, for example: finding your way in an unfamiliar place; • recognising peoples’ faces; • playing ball games; • looking at the architectural features of a building; • monitoring the ground while walking. • ‘Visual tasks’ are activities that require the brain to collect information from some specific part of the visual surroundings. The term is used commonly in the context of the office, classroom or factory, but the principles of task lighting are more general: we carry out visual tasks all the time, mainly subconsciously. The normal process of perception is abstracting what we need to know from what we see, and this is also the essence of task performance. Task design is therefore not a special part of lighting activity; it is something applicable across the whole scope of design. In practice, this means that techniques that are usually discussed in the context of workplace performance can be used advantageously whenever it is important for something to be visible. Size, brightness and contrast Task illuminance – the amount of light falling on the task – affects the speed and accuracy of working. But only up to a point: if you a reading by the light of a single candle then adding a second candle will help greatly; if you are already in a bright room, doubling the illuminance on the page may give no perceptible improvement. There is a point beyond which additional light makes little improvement to the speed and accuracy of task performance. Where this point occurs depends on the size and contrast of the task detail: with small grey print on grey paper, a much greater illuminance is required before you reach your optimum performance than when reading large black type on white paper; nor will your performance be as good however much light you add. Try reading the small writing in Figure 1.14 under different levels of light, or looking at it with half-closed eyes. Figure 1.15 shows the relationship between performance and task illuminance. The most important conclusion to be drawn from it is that, no matter how much task illuminance is increased, the speed and accuracy of carrying out a visually difficult task is less than that of one with greater contrast and bigger detail. This means that designing the task and its surroundings to increase these factors – with, for example, the use of directional lighting to enhance solid forms, the systematic use of colour, and the use of optical aids such as magnification – is more effective than increased illuminance alone. Notice in the lowest two items in Figure 1.14 how colour contrast can enhance visibility. Illuminance/performance curves such as those in Figure 1.15 are average values: they are the lines that best fit a broad scatter of measurements. In experimental data, there is much variation between individual subjects, even when factors such as ageing, motivation, adaptation and visual handicaps are taken into account. Any attempt to make recommendations for task illuminance also depends on judgements of value: do you set the level at 90% or at 99% of optimum performance – one might imply an illuminance ten times the other? And how do the tightly controlled simplified tasks used in the laboratory relate to the varying and complex visual fields of the normal workplace? For purposes of standardisation, such judgements have to be made, and schedules of recommended illuminance such as the list at the end of this chapter are the bases of lighting design throughout the world. They ensure that minimum standards are achieved and they serve as a benchmark for contractual purposes and for analysing factors such as energy consumption. But the sensitivity of task illuminance values must be interpreted in the context described: a doubling of illuminance from 500 lx to 1000 lx may have some effect on
- 33. 20 D A Y L I G H T I N G the performance of a visually demanding task, but an increase from 500 lx to 550 lx is likely to remain imperceptible. There is some evidence that a lower illuminance is required from daylight than from electric lighting, to maintain a given level of performance. The reasons for this are not certain: it is possible that both physiological and psychological processes are involved. It is known, for instance, that performance is better when the colour rendering quality of the source is improved; the flow of light from a side window is soft but directional, giving good three-dimensional model- ling; it is also true that people prefer daylit rooms, so improved motivation might be a factor. The principal aim of lighting design is often taken to be the provision of plenty of light. Possibly, this is because the development of lighting technology has, throughout history, been a search for increasingly efficient sources. It is also a view reinforced by the fact that most standards use illumin- ance, a measure of light quantity, as the principal criterion of lighting merit. But to think in this way is to miss the point completely: the purpose of lighting is to convey information. The light that reaches our eyes varies in time and direction, the result of interactions with surrounding surfaces. From this variability, we are each able to construct a mental model of our own immediate world. It is helpful to think of our senses not as instruments that measure energy, like photometers, but as receivers of signals. It is then clear that the essential requirement with respect to light intensity is that the illumination reaching the eye has sufficient energy to carry the signal. This gives a theoretical basis for performance/illuminance curves such as those in 1.14 Size, brightness and contrast are the three primary characteristics of visual tasks that affect visibility. 1.15 The relationship between illuminance and task performance. The curves are trend lines drawn through very scattered data. Based on work by Weston [50].
- 34. C R I T E R I A O F G O O D D A Y L I G H T I N G 21 Figure 1.15. The more information to be carried, the greater the signal bandwidth needed. Where the spatial resolution must be high (that is, where fine detail must be seen) or if sensitive discrimination is required between different levels of brightness or colour (where contrast in a visual task is small), or when the visual field is changing rapidly, a carrier of more energy is needed than when a simple clear pattern is the information conveyed: this is illustrated by the differences in the graph between lines representing different size/contrast combinations. It follows also that if a signal is already suffi- ciently strong to embody all the information required, no advantage will be gained by increasing its energy: this is shown by flattening of the curves as illuminance increases. Geometry Good task lighting design does not begin with numbers. When the aim is to achieve comfort coupled with the best possible visibility of a task object, the design strategy is to answer four groups of questions. The first two define the problem: What characteristics of the task need to be visible? Is it 1 a surface pattern, such as a printed page? The three- dimensional shape of an object? The surface texture? Who is doing the task? Is the person for whom we are 2 designing very young or old? Does he or she have normal eyesight? Any physical handicaps? Is the task repetitive over a long period, or short in duration? Is it done in a fixed position – sitting or standing – or does the person move around? The two questions draw out the solution: What form of lighting best enhances the critical character- 1 istics of the task? Should there be a beam of light just skimming the surface to exaggerate texture, or diffuse light to mask it? Is the surface pattern more important than the shape of the object? Is the surface shiny or matt? Is colour important? Is there movement? Where should the light sources be, in relation to the task 2 and the viewer? What is the background? Is any screening needed? With daylight, this last group of questions is crucial. The geometry of the layout – the positions of windows in relation to the tasks and positions of users – predominantly determines the quality of workplace lighting. Where the lighting is faulty – with users feeling discomfort or being unable to work with the speed and accuracy that they should achieve – the fault is usually due to the geometry of the layout. Worksheet 12 gives a diagnostic procedure for finding the causes of discomfort or weak performance due to poor workplace lighting. Faults fall into five categories: Glare from a direct view of the source. 1 The sky or other bright objects are visible close to the task in a user’s line of sight. If the contrast is sufficiently great, this can be uncomfortable; but performance can be lessened by bright views close to the task even when there is no discomfort. Glare from reflections. 2 Sources of light reflected in shiny surfaces cause discomfort or impair performance by being bright patches in the field of view. Task contrast reduced by reflections 3 . Bright objects reflected in the task area itself act as a veil of brightness over the detail of the task. This is often a serious problem with VDUs in offices and with whiteboards or traditional chalkboards in classrooms, as in Figure 1.16. The person in Figure 1.17 is handicapped by several lighting faults that would impair his visual ability by reducing the effective contrast in the visual task: he is facing a bright sky; sunlight falls on his desk; there are shiny reflections in the book he is reading and in the surrounding desktop. Dazzle 4 . The brightness of the task surface is so great that the eye cannot adapt to it comfortably. Bright sunlight on white paper is a common cause of this in schools and offices. In industry, processes such as welding require protective screens. Excessive brightness can be dangerous in the short term owing to accidents from temporary blindness. Frequent or prolonged exposure causes permanent eye damage. Low illuminance 5 . Insufficient light falls on the task. If the original lighting installation was adequate, low illuminance on task areas can be the result of shadows – from rearranged furniture, for instance, or where a user sits with his back to a window, blocking daylight that should fall on the work surface. A frequent cause of inadequate illuminance is poor building maintenance – failure to replace lamps, to clean luminaires or to repair blinds. The practice of keeping blinds permanently closed to exclude
- 35. 22 D A Y L I G H T I N G sunlight or reduce sky glare is also a common cause of low illuminance. The geometry of source–task–user is a factor in all these categories of fault. Its importance cannot be overestimated: an apparently minor change in a user’s working position can transform good task lighting to bad, and vice versa. There is a simple rule which applies to most situations: windows should be to the side of users; the lines of sight of users should be parallel with the window wall. When a person is using a VDU, or working with papers at a desk, or using machine tools, there is a high risk of diminished task visibility when a window is either directly behind or directly in front of the user. The corollary of this is that if windows occupy a large fraction of two adjacent walls, good task lighting is very difficult to achieve. In such cases, a practical solution is to lower the blinds of all windows in one orientation. This again emphasises the rule that good daylighting depends on decisions made in the early design stages of a building. It is the block form of a building and its orientation that determine the availability of sunlight, the view and the amount of skylight falling on windows; and it is the shape and layout of rooms and the location of windows that determine the extent to which the incident daylight can be used as workplace lighting. People vary very much in the daylight illuminance they choose to work in. If they can freely adjust window blinds and electric lighting in their workplace, they usually change the settings little after they set them up initially when moving into the space. Those who work primarily on computers tend to set up a lower illuminance on the desktop than those who use computers occasionally. This may occur for several reasons, particularly (a) to reduce distracting brightness 1.17 The person sitting here suffers from major faults in the lighting. He faces the bright sky, he has sunlight falling on his task area, and his vision of the task will be reduced by shiny reflections. 1.16 Veiling reflections on a book and a VDU screen. The bright fuzzy pattern in the screen is the reflection of a view though a window.
- 36. C R I T E R I A O F G O O D D A Y L I G H T I N G 23 from a direct view or reflection of windows or luminaires, and (b) to achieve a lower overall background brightness to the screen. People with impaired vision Older people and those with impaired vision from other causes need special consideration. Visual impairment has several symptoms, varying with the cause of the disorder. These are common problems: Reduction in the fraction of the light entering the eye that 1 reaches the retina. Owing to yellowing of the lens, the shorter wavelengths of the spectrum are especially attenuated, so the sensitivity to blue light is seriously reduced. Slower responses. Brightness adaptation is slow, and 2 so is focusing on objects. Reduced colour saturation and reduced contrast. 3 Increased sensation of glare. 4 In most cases, but not all, higher illuminances are required on visual tasks; the optimum level is typically double or more the amount needed for the same task by young people with good vision. More important still are two requirements: high contrast between object and background, and within visual tasks; and a minimising of bright sources that could be glaring. As in task design generally, enhancing contrast by changes of surface colour and clarifying the task detail can have a greater effect than increases of illuminance. ‘Too much daylight’ It is comfortable reading a book outside provided that it is not in direct sunlight. If the sun is 60° above the horizon (approximate solar elevation at noon in summer in the UK), the illuminance on the ground from sun and sky can exceed 100 klx (100,000 lx). That illuminance on the white pages of a book is dazzling. With the sun hidden by cloud, the average horizontal illuminance is typically 40 klx at that solar elevation. For most people, this is no longer dazzling. Compared with these external values, illuminances inside a building are small: 500 lx is the typical recommended value in a general office. Nevertheless, desktop illuminances of only three or four times the recommended amount have been judged as ‘too bright’ in some field studies. Clearly this is not due to the illuminance itself, a value maybe one-twentieth of an acceptable external illuminance. What it shows is that to achieve a high value of daylight in a working position, there is a risk of discomfort or visual disability from direct glare or glossy reflections. The problems are likely to be more severe if there is a large brightness difference between surfaces at the back of the room and those close to windows. Peripheral and central vision We depend on our peripheral vision to warn us about any change in the space around us. When we look at something, we move our eyes so that the centre of interest is focused on the fovea, a small area in the centre of the retina. Peripheral vision is the rest of our visual field, everything that is focused on the retina outside the fovea. Much of the time we are not conscious of it. The peripheral field remains below the level of awareness until something within it changes. Then we notice something and direct our interest, and our foveal vision, towards it. The periphery of the visual field is especially sensitive to movement. We continuously monitor our surroundings; we become aware of anything moving into our visual field. If the ground surface changes as we walk, we glance downwards; a large unexpected movement overhead makes us shield our head. Because of the nature of our peripheral vision, flashing warnings are more noticeable at the edge of vision than in the direct gaze. Having the central field of vision only is like using a bright narrow-beamed torch in a large dark unfamiliar room: you can see detail clearly but it is hard to gain a sense of the place as a whole. A dim diffuse light in the room might be inadequate for reading small detail but you can see the form of the room and sense its character. This is an analogy of the part that the outer area of the visual field plays in the perceptual process. Complete vision requires both parts. So task lighting design does not stop at the edge of the visual task. Firstly, as we discussed above, the brightness and colour of the immediate surround to the task affect the visibility of the task itself. Secondly, the nature of the
- 37. 24 D A Y L I G H T I N G peripheral field can enhance or distract from concentration on the task. Rapid movements and flickering lamps interfere with performance. Conversely, a task environment that conforms to expectations, that is ‘normal’, is supportive. Daylight, with its variability and the information that this gives, is part of what is ‘normal’ in many room types. Brightness adaptation The human body is able to change physiologically as the immediate environment changes. When conditions cool, the blood vessels near the skin rapidly become constricted to minimise heat loss; in hot conditions, they dilate, and the skin perspires, to maximise cooling. There are also long-term physiological changes that occur when a person goes to live in a warmer or cooler climate. The eye adapts to motion and to particular shapes, to colour and to brightness. These latter two are particularly relevant to daylight. Over a period of an hour or so during a calm sunny afternoon, the light entering a window may fall to a quarter of its initial amount and its colour may vary from a cool blue to a warm white; but, even if you are sitting working in daylight at a desk near the window, you are very likely not to notice these changes. In signal processing terms, the adaptation of the eye is like a filter that blocks slow changes of brightness and colour. Three mechanisms of the eye are used in brightness adaptation. The first is the opening and closing of the iris; this is a fine adjustment comparable to the way a photographer reduces the camera aperture to obtain greater depth of field when there is ample light. The second is a neural process, transformation of sensory data in the eye–brain system; this is responsible for the almost immediate adaptation that occurs in situations where the luminance range is not large. The third mechanism is the bleaching out and regeneration of pigment in the photosensitive cells of the retina; with this, adaptation from dark to light is rapid; the regeneration of pigment needed for light-to-dark adaptation can take up to an hour. Combined, the mechanisms give a range of sensitivity that enables us to see in conditions from starlight to bright sunlight. Figure 1.18 illustrates this. The reduced visibility of a task when light from bright objects in the background falls on the eye is the result of inappropriate adaptation: in photographic terms, the task area is underexposed because the background illumination has reduced the eye’s sensitivity. There are situations where the brightness adaptation of users must be controlled. The lighting of roadway tunnels must provide zones of intermediate brightness as drivers enter and leave. In a cinema, where users may enter from a daylit street, the sequence of spaces from the entrance, through the ticketing area, the foyer and the approach to the auditorium should be a progression of reducing brightness. The same strategy may be necessary in an art gallery, where the illuminance on the pictures displayed has to be low to minimise radiation damage. The visitor is taken through a sequence of spaces where the brightness of the displays gradually diminishes and users’ vision becomes increasingly sensitive. There are two requirements of spaces entered by people adapted to a higher illuminance. The first is to ensure that the light falling on their eyes is minimised, so their visual sensitivity is enhanced; the second is that essential objects are sufficiently bright to be well visible. These requirements do not necessarily conflict: the illuminance on the eye from a source depends on its luminance and its angular size. So the aim is to provide small areas of relatively high luminance that enable users to find their way, gain information and appreciate the displays. The same applies to emergency lighting that enables escape when the normal lighting fails. At very low lighting levels, colour can be used selectively. 1.18 Adaptation to low levels of brightness. Subjects sit in a dark room after being adapted to strong light. At intervals, they are shown short flashes of light of different luminance. The graph shows the lowest luminance they detect plotted against the time they have spent in darkness. The angle in the curve indicates transition between the photoreceptors active at daytime levels of light (cones) to the more sensitive cells of the retina active at low levels (rods). Based on work by Arden [51].
- 38. C R I T E R I A O F G O O D D A Y L I G H T I N G 25 The eye’s photoreceptors that operate at daytime brightness are relatively much more sensitive to light at the red end of the spectrum than are the receptors that provide night vision. Red lights can be used as beacons or warning indicators without significantly affecting dark adaptation. Most of the ways of dealing with brightness adaptation depend on the basic planning of the building – the sequence of display spaces in an art gallery, the location of the entrance and the layout of foyers in a cinema, the views from inside to outside. Again we reach the conclusion that successful lighting in architecture depends on decisions made at early stages of design. Discomfort glare Glare can be thought of as optical noise, masking the information sought. If intense, it causes physical discomfort. In large rooms, such as open plan offices, a desk worker may be able to see row upon row of ceiling-mounted lumi- naires; if these are bright in the direction of the viewer, the result can be strong discomfort. The glare can be eliminated by choosing luminaires that emit light predominantly down- wards; the luminance of the side of the fittings is then low. But a strongly directional flow of light is often unsatisfactory in a workplace: it gives bright reflections in horizontal desktops; it casts hard shadows that can impair task visibility; it can give unattractive modelling, especially of people’s faces; and more luminaires are necessary because they must be spaced more closely to achieve uniformity of illumination. A better luminaire output distribution is found when the peak intensity of the light output is not vertical but diagonally downwards and coupled with a sharp cut-off of light towards the horizontal. It is also an advantage to spill some light onto the ceiling. Research on glare has focused on quantifying the level of discomfort. This led to the concept of a ‘glare index’, a formula that allows alternative designs for the lighting of a space to be compared numerically. Using laboratory studies of peoples’ reactions, it was found that the degree of discomfort experienced when a subject was exposed to a small bright light depended on four factors: the luminance of the light source • the size of the source • the luminance of the background • the angle of the source from the subject’s line of vision. • The first two have a positive association with discomfort: as source luminance and size increase, discomfort becomes greater. The latter two reduce discomfort as they increase. This implies that discomfort glare is, in effect, the result of excessive contrast within the visual field, a function of source luminance against the luminance of the background. The glare from a source can be reduced by making the background brighter. The same four parameters are found to be important factors in glare from large sources, such as windows, although the glare index equation changes as sources get bigger. Daylight glare calculations have not been widely adopted in practice. Existing formulae are not good predictors of peoples’ reactions to window glare. If a large number of subjects are asked to describe the discomfort they experience in various situations, and if glare indices are calculated from size and luminance measurements taken in each situation, a graph plotted from the results shows a wide scatter. There must be other factors than the four given above that affect the sensation of discomfort from a glaring window. These include the age of the viewer, as we noted earlier. The brightness pattern of the glare source is a factor: it is not enough to measure only the mean luminance of a window. A large uniformly bright screen is judged to be less glaring than a non-uniform screen that gives the same illuminance at the viewer’s eye; and some patterns, such as black-and-white striations, can be very much more uncomfortable. It is not purely photometric characteristics that affect the sensation of discomfort: the viewer’s interest in the glare source influences the degree of discomfort. Very bright television screens carrying an interesting picture are judged less glaring than blank white screens of the same mean luminance. Windows looking out on to an extensive view are less glaring than those looking onto the blank wall of an adjacent building. Views of natural scenes – hills, trees, water – are found to be less glaring than those of buildings, roads and the hard urban landscape. Such results from laboratory studies, in which subjects assess glare from scenes matched in brightness and luminance pattern, show that the sensation of discomfort is moderated by our interest in the cause of it, and whether we have a prior liking or disliking of the situation.
- 39. 26 D A Y L I G H T I N G These research findings are further evidence that human response to light is influenced by the information that the light carries. There are many analogies in other situations. We tend to be more disturbed by a neighbour’s noise – a barking dog, for example – than by our own, and sensitivity is increased further if that sound has already been the subject of complaints. Calculations of glare can be helpful, but they must not override common sense. A late-afternoon sky is beautiful and the beam from the setting sun that falls on the window gives pleasure, even though the glare index would predict it to be intolerably uncomfortable. Conclusions for design The essence of good task lighting is the geometrical 1 relationship of task : light source : viewer. Firstly, light must fall on the task at an angle that enhances visibility of the object, but it must not fall strongly on the eyes of the viewer. Secondly, bright sources of light should not be visible to the viewer from reflections in and around the task. This imposes constraints on the layout of a daylight room, especially with side windows. Generally, viewers’ lines of sight should be parallel with the window wall. Users need to control their workplaces, to adapt to 2 changing conditions. They must be able to control the entry of direct sunlight and to switch supplementary light sources on and off. The quantity of light falling on the task area must be 3 adequate for the task. In rooms of at least medium size, supplementary electric lighting is usually required. If users are visually frail or handicapped, special lighting 4 may be used to enhance their performance, and the task itself may be altered to enhance the size of detail and to increase contrasts. Most older people prefer higher levels of illuminance than young people. Display Good lighting in a shop or an exhibition does three things: it establishes the nature and character of the place; it draws the attention of viewers to the items on display; and it enables the users to see clearly the detail within these items. So far in this chapter, we have covered the first and last of these things; this final section looks at display lighting, especially the use of daylight. Display lighting is the use of light and colour to draw and hold the user’s attention. It is a primary requirement in museums, galleries and shops, but it is a consideration in almost every situation. It is found at all scales, from the floodlighting of a historic city to the layout of controls in a car. As a source of light for display, daylight has qualities quite different from those of any artificial source: the high intensity of the sun’s beam; the large angular size of the diffuse sky; variation in brightness associated with natural events; and variation in colour coupled with excellent colour rendering. But daylight is difficult to control. Throughout the world of optics, the larger the source, the larger the optical devices required to focus its output. The most common technique of display lighting is to make the object on display brighter than its surroundings, and this is usually achieved with the precise narrow beams of spotlights. Skylight cannot be focused in this way and, in addition, it is cumbersome to control in intensity. Shopping malls and other large spaces Many shopping malls have large windows, usually in the form of rooflights. These give the space a daylit appearance, which is popular. Displays of merchandise, though, are almost invariably lit with electric sources, and so are posters, banners, signs and other features in the public areas. The crucial part in the design of such a space is the treatment of intermediate conditions: in time, as the daylight fades, and spatially, in those areas for which the daylight is inadequate. There is a phenomenon of perception that can be employed here: if a strong source of light is visible, there is a tendency to assume that all the ambient light is due to this source. If an atrium has high windows and in addition there is high-level electric lighting providing a downward flow of light of similar colour to the daylight, the floor and walls of the atrium can seem daylit even if the illuminance from the lamps
- 40. C R I T E R I A O F G O O D D A Y L I G H T I N G 27 is as great as that from the windows. It ceases to work when the external daylight falls to a level inconsistent with the indoor illuminance, or when the electric lighting masks the spatial variation of light from windows. The guideline remains: preserve the natural variation of daylighting. So a strategy for daylight design of buildings such as shopping malls and for large atrium spaces in general is as follows: Establish the daytime appearance as being a daylit space. 1 Supplement the daylight in intermediate zones with luminaires that broadly mimic the distribution of light from the window. Create distinctly different daytime and night-time modes. 2 The junction between them could be slow and gradual or it could be an event with orchestrated changes as lights switch on and off. Several lighting modes could be set up: winter daylight, summer daylight, dusk, early evening, late night. Use visible electric sources to create a hierarchy of display 3 brightness, the highest levels being on the most important items displayed. Do not aim for a uniform illuminance. The amount of electric lighting may have to be greater in daylit areas than in those that receive little natural light, but it is normally necessary to ensure that deep spaces opening onto a daylit atrium are sufficiently well lit to avoid a dark cave-like appearance. This strategy of using daylight to establish the fundamen- tal character of a space and to use electric light in two ways, to supplement daylight subtly and to provide display and task illumination overtly, is powerful and widely applicable. Galleries and museums How a work of art is perceived, what it means to the viewer, is hugely influenced by the situation in which it is viewed: an altarpiece by Tintoretto seen in a Venetian church is an experience quite different from that given by a similar painting hung in a gallery; so is the sculpture on the pedi- ment of a Doric temple seen on a Mediterranean island, compared with a reproduction of it on the façade of a nineteenth-century commercial building in a northern European city. It is a strong argument that a work of art is best viewed in the place for which it was originally created. If this is not possible or desirable, we could suggest the following principle: A work of art is best viewed in a luminous environment similar to that for which it was created. We shall adopt this as a working rule and examine its implications. The first conclusion is that paintings and other objects produced before the mid-nineteenth century were most likely to have been produced, used and exhibited in natural light; and probably this would not have been the controlled daylight of the Victorian art gallery but the inconstant unpredictable light of the church or the walls of the patron’s villa, or the civic building. The second conclusion is that this lighting might not be very good by modern standards of task and display design. The type of place where a painting was first shown was often something quite different from an exhibition of pictures, and a painting that we now consider to be of major importance might have been just one of many items. Furthermore, we have sources and luminaires that were not available when the painting was made. We can focus light onto a picture, enhancing the initial impression of a piece and making the detail of the painting far easier to see. This in turn has affected our expectations of how works of art should be displayed. There is, however, a factor that can override all considerations of display: this is the need for conservation. Light, as radiant energy, causes organic materials to deteriorate. Those affected include leather, fabrics and paper; they also include some of the pigments used in paint. Pigments change differentially: some fade rapidly, while others, particularly mineral colours, are unaffected. The result is that the balance of colour in a painting changes gradually and irreversibly with exposure to light. Especially sensitive are works such as old watercolour paintings and Japanese woodblock prints. Most national art galleries and many conservation organisations have a legal duty to preserve their collections for the next generation. They also have a duty to make the works available for the present generation to enjoy and
- 41. 28 D A Y L I G H T I N G to study. The curator thus has to reconcile four conflicting aims in the display of a work of art: To illuminate the work and its surroundings in a historically 1 accurate way; that is, in a way that would match the expectations of the artist. To display it so that the impact of the work is maximised. 2 To display it so that the detail of the work is most clearly 3 visible. To cause no damage or change to the work. 4 The solution depends on the nature of the object, its value and importance, its robustness to damage, the purpose of the exhibition, and for whom the display is presented. We can begin the process of finding this solution by asking three broad questions: What constraints are imposed by requirements of 1 conservation: what is the maximum acceptable illumi- nance on the object and the period for which it is to be displayed? What is the purpose of the exhibition: for example, are the 2 objects displayed for sale, or is it a theatrical display, a reconstruction of a historical scene, or a scholarly presentation? And who are the viewers: children, tourists, the general public, academic students? What is the ideal form of lighting for display: for example, 3 direct sunlight for stone sculpture, or natural room lighting for pictures, or small-scale individual lamps for miniature objects? The answers to these questions should point towards the degree to which daylight is used in the display space. Table 1.1 summarises the possibilities. A conclusion that can be drawn from the table is that daylighting should not be considered separately from the layout and form of the building as a whole, or from the design of electric lighting. Here is an example. People entering an exhibition have to make a transition between daylight outside and much lower levels of light in display spaces. On a bright day, the ratio of the mean external illuminance to the mean illuminance in a gallery displaying light-sensitive materials can be 2000:1. Significant brightness adaptation is needed; therefore the route of visitors should be gradual through a sequence of spaces of decreasing brightness. The extent to Table 1.1: Daylight in galleries and exhibition spaces Advantages for display Disadvantages Windowless interior. Permits the creation of a complete environment, and use of the full range of display and theatrical techniques. In most cases, unrealistic in relation to the original environment of art works. Disadvantages of windowless rooms generally. Windows providing general room lighting and views out; supplementary lighting on pictures. Appearance of a daylit room. May simulate the original ambience of an art work. Depends on the basic plan form and orientation of the building. Difficult to achieve very low illuminances on light- sensitive materials. Side windows providing illumination on art works. May simulate the original ambience. Good colour rendering. Good modelling of three-dimensional form. Difficult to avoid glare and bright reflections in art works. Difficult to control illuminance. Specially designed roof lights illuminating art works. Basic form of nineteenth- and twentieth- century picture galleries. Was the setting for which many works were produced. Good colour rendering. Direction of light reduces shiny reflections. Daylight can be controlled with louvres and blinds. Can be supplemented with electric lighting. Institutional appearance may not be appropriate. General appearance of room can be dull. Incoming daylight can be controlled to the extent that all the natural variation is lost. Semi-outdoor space, highly glazed. Can be used to simulate the external environment of art works. Direct sunlight available. Thermal attributes of highly glazed spaces. Unsuitable for light-sensitive materials.
- 42. C R I T E R I A O F G O O D D A Y L I G H T I N G 29 which this is possible depends on the basic form of the building; and it is a constraint on the layout of any exhibition in the building and on the electric lighting. The prime reason for the use of daylight in buildings such as art galleries is the quality that we have argued is important in all buildings: its variation and the meaning it has to the viewer. Moreover, natural lighting provides a powerful means of connecting our present experience of a work with that of its artist. Objects and background Good display lighting design begins with the objects to be displayed. Like the design of task lighting, there are questions to be posed: What is to be enhanced? For instance, is it silhouette? 1 Colour? Texture? Surface pattern? 3D form? Who is looking at it, and from where? What is the back- 2 ground? Does the object have to grab attention in a complex visual environment? Is the object or the viewer in motion? What are the relative locations of viewer, object and light sources? What is the balance between the need to attract attention 3 to an exhibit and the need to see it in detail? The answer to the third of these questions depends on the purpose of the display. It differs between a shop window and a museum. In art gallery design, it is necessary to compromise between the differing visual requirements of display and assimilation. For example, pictures displayed on a white, evenly lit wall attract immediate attention, especially if they widely spaced. There is an economical approach to the renovation of an old building as a gallery: paint the walls, ceiling and beams – all the upper surfaces – white; strip the floor surface to its original wood or stone; provide plenty of daylight and many small spotlights; and let pictures alone provide strong colour. It is a strategy used by many small shops and restaurants. It is found in the traditional streets of the Greek islands, as in Figure 1.19. But when a picture is seen against a bright white back- ground, the apparent range of colours in the picture itself is contracted. This is especially noticeable in greyscale images. The photographer Ansel Adams, known for his technical skill in creating prints with a consistent tonal scale over the whole black–white range, preferred to display his work on a back- ground with a reflectance of 0.18, a mid-grey close to the average reflectance of the images. It is a decision that the exhibition designer or the gallery curator must make: setting pictures on a strongly contrasting background emphasises their outline shape and enhances their visibility as objects in the room, but at the cost of a smaller tonal range or reduced apparent contrast within the pictures themselves. With a background consistent with the tonal range of the pictures, the opposite is true. What choice 1.19 White surrounding surfaces make coloured patches prominent and enhance the silhouette of superimposed objects. There is much interreflected light, increasing the sense of brightness, a characteristic of traditional Greek villages. Rhodes, Greece
- 43. 30 D A Y L I G H T I N G is made depends on the nature of the display: in a shop, the need is for the objects to catch the glance of a potential buyer; in a national museum, the aim is to display the true quality of the work. Conclusions for design The designer’s approach can be summarised by the checklist in Table 1.2. 1.20 The lightness of the surround affects the degree to which an image stands out and it also affects the apparent contrast within the image. Table 1.2: Checklist for the beginning of display design 1 What is the purpose of the display? To sell? To entertain? To educate? To shock? 2 What is the overall character of the display? Cool and understated? A complete enclosing environment? Noisy and multicoloured? Set within an existing architecture? 3 Take the objects on display. Decide what characteristics should be enhanced, what limitations there are on lighting (maximum illuminance, security, etc.). Decide what background they should be seen against. 4 Consider the people viewing the display. How will they look at the objects? How far away? For how long? Are they static or moving? Are they families? Children? ...
- 44. 31 This chapter introduces the physics of lighting. It can be read as a whole, you can dip into it to read about topics that are unfamiliar, or you can skip it altogether and use it as a reference later. It is structured in a way that allows you to look up a particu- lar point, and go into the detail only as far as you need. If you read the first part of each section, you should gain a working knowledge of the main ideas and the words used to describe them; if you work through the chapter as a whole, you will cover much of the theoretical basis of illumination engineering. A few simple principles underlie the subtle and complex patterns of brightness and colour within the translucent foliage of a plant – or in a cloudy sky or a daylit room. If you know the rules, you can explain why a particular lighting effect occurs or predict the appearance of a finished scheme when the design is no more than a sketch. You can also look at a rendered computer image and tell whether or not it is realistic. two What light does 2.1 The complex variation of luminance and colour in the foliage can be explained by simple processes of reflection and transmission of light.
- 45. 32 D A Y L I G H T I N G Luminous energy The principles described in this chapter apply to a physical world measured in millimetres, metres or kilometres – several orders of magnitude greater than the wavelength of light, the scale of people, buildings and towns. It is necessary to state this because the rules that predict the behaviour of light depend on the scale at which it is observed. We are fortunate: at the dimensions of the human world, light can be treated as just a flow of energy, a simplification not possible at the scale of quantum mechanics or at the scale of cosmology. What we describe as light has no fundamental physical meaning, but is defined by human vision: it is simply radiation to which the eye is sensitive. Radio waves are electromagnetic radiation; so are ultraviolet light, x-rays and gamma radiation. They vary only in their wavelength, (which is usually measured in nanometres: 1 nm =10−9 or 1/1,000,000,000 of a metre). We have various names for parts of the electromagnetic spectrum: the part we call ‘light’ is the band of wavelengths that are strongest in the solar radiation that reaches the earth. We have evolved in the rays of the sun and our bodies have grown to use solar radiation in the most efficient way. There is an inherent problem in defining light in terms of the human eye: none of the normal physical units of energy can be used to quantify it. Light has, therefore, its own set of units. They are not used in other contexts and are not everyday measures – like kilograms, watts or metres – so we do not have a familiar sense of their meanings or their magnitudes. They need to be learnt. In all, there are four units of light and they will be introduced during the course of the chapter when they are needed. They are summarised in Worksheet 13. The first lighting unit is the lumen (lm), which describes the rate at which luminous energy is flowing out of a lamp or through a window. Its physical equivalent is the watt (W), which can quantify the rate at which electrical energy is consumed: an incandescent lamp might use 100 W and emit about 1200 lm. A candle emits about 13 lm; a window in sunlight might admit 65,000 lm per square metre of glazing, but this depends on the height of the sun and the angle at which it strikes the window. The ratio of the light output from a source to the total radiation emitted is known as luminous efficacy, measured in lumens per watt (lm/W). The luminous efficacy of an incandescent lamp is low, only about 13 lm/W, because most 2.2 We sense the radiation emitted by a candle in two ways: as warmth and as light. Originally, a candle was used as a reference for quantifying light. In present- day units, the flow of light from a candle is about 13 lumens.
- 46. W H A T L I G H T D O E S 33 of the electric energy consumed by the lamp is emitted as heat; fluorescent lamps have a higher efficacy, typically about 80 lm/W. Light is measured by photometers, instruments that respond to radiation in the same way as the human eye: at daytime levels of ambient light, the eye is insensitive to wavelengths shorter than about 380 nm, has a maximum response around 555 nm, then gradually reduces in sensitivity as wavelengths increase to 780 nm, above which it is again insensitive. If, mathematically, a lamp output in watts needs to be converted to its light output in lumens, the spectrum is divided into narrow bands, the energy in each is multiplied by the eye sensitivity there, and the results are added up. Light in the atmosphere A projector beam can be seen in a smoky cinema but not when the air is clear: where there is pollution, particles suspended in the air divert a fraction of the beam and some stray light reaches the eye. It is not just pollution that causes scattering. The sky is luminous because the solar beam is scattered by the molecules of gases as well as by small particles in the atmosphere. These atmospheric components vary with weather, time and place, so the sky changes in brightness and colour. The sunbeams in Figure 2.3 appear because water droplets in the air divert some of the sunlight that flows between gaps in the cloud layer. The sky is the atmosphere made visible. It is not something above us, separate from us: we are within it, moving through it, changing it, breathing it. ‘Sky’ lies between us and everything we see. The distant peaks in Figure 2.4 are lighter and bluer than the nearer rocks because light reflected from their surfaces is scattered while other light passing through the intervening volume of atmosphere is diverted towards us. 2.3 Beams of sunlight made visible by dust in the atmosphere. Desert, Iran
- 47. 34 D A Y L I G H T I N G The greater the density of particles or droplets in the air, the more the light is dispersed. In a very foggy atmosphere, a bright halo surrounds every source of light. This scattering attenuates the beam, making it weaker with distance. The density of particles also affects what we can see: in a thick fog, we can see only a few metres ahead because nearby droplets hide everything further away. The combination of diffusion of light and reduction of the distance of vision is the cause of the characteristic patterns of sky brightness that occur with particular weather conditions. The cloudless blue sky is the result of light scattered out of the solar beam by the molecules of the atmospheric gases. If the sun is directly overhead in a clear sky, we see the intense brightness of the solar disc surrounded by a flare that declines into deep blueness as the angle of vision from the sun increases: most of the scattered light is diverted out of the beam by only a few degrees. But the brightness of a clear sky increases again just above the horizon, because, although only a small fraction of the light is scattered to the viewer at this angle, there is a very long view through the atmosphere. Molecular scattering varies greatly with wavelength; the blue end of the spectrum is affected more than the yellow– red. This creates the blueness of the upper sky; the deeper the colour, the clearer the atmosphere. The term ‘turbidity’ describes the scattering due to processes other than molecular – for example the effect of water droplets or solid airborne pollutants. These particles are larger than gas molecules, usually larger than the wavelength of light, and they re-mix the spectral colours. During the day, a cloudless sky of high turbidity looks much whiter than an unpolluted dry atmosphere. 2.4 The blueness of distant mountains is the result of light scattering along the line of sight. Hua Shan, Shaanxi province, China 2.5 The characteristic brightness pattern of a clear sky is caused by molecular scattering in the upper atmosphere.
- 48. W H A T L I G H T D O E S 35 A heavily overcast sky usually contains several layers of cloud, each reflecting and diffusing the downward light, and each darker within than the layer above. A directly upward view from the ground tends to penetrate to brighter clouds than an oblique sightline; so, seen from a point on the ground, there is an increasing brightness from horizon to zenith. This brightness distribution that occurs on dull rainy days, the weather conditions when daylight tends to be at its minimum, has long been used as a reference sky for daylight calculations in a standardised form. There is more on this in Chapter 3. The longer the atmospheric path of the sun’s beam, the more the attenuation and the broader the directional separa- tion of colour. A beam along a path almost parallel with the surface of the earth is seen as the setting sun. The rays have a long path through the atmosphere, so there is much scattering. Orange–red can dominate the view towards the sun, as in Figure 2.7; the sky in the opposite direction would be deep blue. In most cases, there is little absorption of light in the atmosphere, only reflection and scattering, so most of the solar energy is preserved. However, in a highly polluted atmosphere, such as in Figure 2.8, particles and droplets suspended in the air absorb light, reducing the brightness of the scene, especially of distant objects. Light on a surface and Lambert’s law Illuminance In Figure 2.9, beams of sunlight make bright patches on the wall. To quantify this, we would take the amount of light (luminous flux, measured in lumens) and divide it by the area on which it falls (measured in square metres). The result is called illuminance, measured in lux (lx): 1 lux = 1 lumen per square metre This is the second of the four units of light and is the one most frequently used to specify lighting requirements. The beam of sunlight in Figure 2.9 falls at a glancing angle on the wall. If the wall could be turned to make a right angle with the beam, the sunlit patch would be smaller but brighter. The angle between a beam of light onto a surface and a line perpendicular to the surface is called the angle of incidence. When the surface directly faces the source of light, the angle 2.6 A heavily overcast sky often has several layers of broken cloud. Th e sky tends to be brighter at the zenith than at lower angles of view, though there is often, as in the photograph, a skirt of brightness just above the horizon. New South Wales, Australia
- 49. 36 D A Y L I G H T I N G 2.7 When the sun is low in the sky, its brightness is attenuated by a long path through the atmosphere. Light at the longer wavelengths, the part of the spectrum towards red, is scattered less than the shorter- wavelength blue. Cornwall, UK 2.8 In a highly polluted atmosphere, solid particles and oil droplets absorb light and reduce contrast. Xian, China
- 50. W H A T L I G H T D O E S 37 of incidence is zero and the illuminance is highest. When the beam falls obliquely, the patch of light becomes larger, and so the illuminance, the amount of light falling on a given area of surface, is smaller. This effect is called Lambert’s law, after the eighteenth-century mathematician Johann Heinrich Lambert, and it is written formally as follows: Illuminance is proportional to the cosine of the angle between the direction of the incident light and a line at 90° to the surface. It can be expressed much more concisely in symbols: ∝ cosq (2.1) Large sources, small sources and ideal sources We know from everyday experience that different types of light source produce characteristic patterns of light. We can recognise not only the presence of a window or luminaire that is hidden from view, but also its location, and its size and type. In Figure 2.10, for example, we know at once that the bright patches on the walls and ceiling are not caused by light from the windows, so we deduce that those protruding brackets are wall-mounted luminaires, shining upwards. Looking at Figure 2.11, we guess that there must be 2.9 Illuminance from a beam of sunlight. The Green Palace, Iran 2.10 Large and small sources: daylight plus recessed spotlights in the ceiling and wall-mounted uplighters. The Orangery, Kew Gardens, London
- 51. 38 D A Y L I G H T I N G windows just out of sight in the wall on the right because we know that the even illumination on the left-hand wall could not be produced by the small candle-like lamps in the chandeliers. In architectural lighting, the size of a light source is crucial. A small lamp and one that is larger in area but less bright can produce the same illuminance at some chosen point, but, photometrically and visually, they differ. The small source looks very bright because all the light is emitted within a tiny area; this gives crisp shadows, but the illumination decreases rapidly with distance. A large source of light producing the same number of lumens looks far less bright; it casts soft-edged shadows, and the distance between source and receiver has less effect. Much of the theory of lighting is based on hypothetical extremes. It asks what would happen if something were taken to the limit – if the source were infinitely small, infinitely large or infinitely far away. We begin by looking at what happens when a light source is very small. Point sources, intensity and the inverse square law Nothing real can be infinitely bright and of infinitesimal size, but many actual sources can, with negligible error, be treated as dimensionless. And if a source is point-like, the beautifully simple inverse square law applies. In symbols, E r ∝ 1 2 (2.2) In words, lluminance is inversely proportional to the square of the distance from source to surface. If a spreading beam of light gives a patch of light 1 metre square on a wall, it produces a patch 2 metres square on a wall twice as far away. The patch area increases from 1 m2 to 4 m2 , so the illuminance (flux divided by area) is reduced to one-quarter of the original value. The inverse square law lies at the heart of lighting calculations. Here is an example: • A projector 3 m away gives 100 lx on a screen. What is the effect of moving it back to 4 m away? • The area illuminated increases by a factor of (4/3)2 , so the illuminance on the screen falls to 100 ×(3/4)2 , about 56 lx. Luminous intensity To fully describe the output from the projector, another unit of light is needed: the total in lumens would not be enough. 2.11 Some of the sources of light are hidden from the camera. Can you deduce where they are from the patterns of brightness on the room surfaces? L’ Hôtel de Ville, Lyon 2.12 Light from a projector.
- 52. W H A T L I G H T D O E S 39 To specify the performance of lighting equipment, especially items such as projectors and spotlights, it is necessary to state how much light goes in a particular direction. This is the purpose of the third of the four units of light, the candela (cd). Luminous intensity can be understood as follows. Picture a tiny lamp hanging at the centre of a transparent sphere one metre in radius. Imagine a circle drawn on the sphere. The intensity of the lamp in the direction of the circle is the number of lumens divided by the area of the circle. If the circle is linked back to the centre, it makes a cone. This cone could be made narrower, to be more precise about direction, but then it would be necessary to take into account the width of the cone. The normal way of doing this is to give the ratio of the surface area to the radius squared. This is called a solid angle, an angle in three-dimensional space, and is measured in steradians (sr). In symbols, w = s r2 (2.3) where ω is the angle in steradians, r is the radius of the sphere, and s the area of the surface patch (which can be any shape – it does not have to be circular). So luminous intensity is defined as I F = w (2.4) The total angle surrounding a point in space, like the lamp in the centre of the sphere, is 4π steradians, so if a lamp emitting F lumens has an output that is the same in all directions, its intensity is F/4π candelas. The reason for the slightly difficult definition of intensity is that there is a simple outcome: the concepts of illuminance, intensity, Lambert’s law and the inverse square law are interlinked. Together, they give the most important equation in lighting: E I r = cosq 2 (2.5) I is the intensity of the source in the direction of the surface, θ the angle of incidence on the surface and r the distance between source and surface. The formula can be used with negligible error when the maximum dimension (for instance the diagonal size of a rectilinear luminaire) is less than one-fifth of the distance, r/5. An infinite plane of light and the concept of luminance Imagine a grey cloudy sky spreading uniformly bright towards the horizon in every direction. The illuminance on the ground might, if you measured it, seem higher than expected: everything looks dull in these conditions. If you walk to the top of a high hill, halfway toward the cloud base, the meter 2.13 Solid angle. 2.14 A uniform sky. This photograph has been modified to remove sky luminance variation but it remains a realistic image.
- 53. 40 D A Y L I G H T I N G reading may change little – getting closer to the source does not seem to affect the amount of light. The key characteristic of a large source is its luminance. This value is the last of the four units of light. Luminance means objective brightness – what a meter reads – rather than the brightness perceived by the eye, which is affected by adaptation and by contrast in the visual field, and is referred to as apparent brightness. The definition of luminance is again linked with the idea of an infinitesimal source. Imagine a bright surface, such as a translucent screen with a lamp behind it. Draw a circle on the surface and imagine another floating in the air just above the surface. The area within the surface patch is s square metres. Assume that F lumens emitted from the surface patch flow through the floating circle. Now imagine the surface patch shrinking until it is almost a dimensionless point. The ratio F/s remains nearly the same, because both numbers are reduced, and the shape of the beam approaches a cone. So, if we take the value to which F/s is converging and then divide this by the angle of the cone, the result is a new concept: intensity divided by area. This is the meaning of luminance, and hence it is measured in candelas per square metre (cd/m2 ). Writing mathematically the limiting process we have just described, luminance is defined as L I s = lim , 0 s → s (2.6) There is a problem, though: how do you measure the area of the sky? The definition of luminance using a surface source makes no sense when the source is volumetric and infinite. To deal quantitatively with sky brightness, we need to look at the situation the other way round. Imagine a surface facing a bright screen and parallel to it. Draw a circle on the screen, as before, and one exactly opposite on the receiving surface. The area of each circle is s and the angle each circle makes from the centre of the opposite circle is ω. Now if ω is quite small, the circle on the screen can be treated as a point source, and the illuminance in the receiving circle by light received from the source circle is E I r = 2 (2.7) By the inverse square law, Equation (2.5) I is the source intensity and r the distance between the surfaces. (The angle of incidence, θ, is zero because the beam is perpendicular to the surface, so cos θ = 1 and we can ignore it.) The intensity of the source is, by definition, s the luminance of the source in the direction of view multiplied by its area, but since w = s r2 we can write E Ls r L L E = = = 2 w w so, (2.8) The luminance of a patch of sky is the illuminance on a surface directly facing the patch divided by the angular size of the patch. The argument becomes rigorous if, as before, we define the equation as the limit when s approaches zero. What it means is that luminance does have a physical meaning when a source is not a surface. Luminance meters work on this principle. In essence, they consist of a photocell, which gives an electrical signal when light falls on its surface; an electrical meter; and lenses or baffles that accept light from only a small angle of view. 2.15 Defining luminance
- 54. W H A T L I G H T D O E S 41 The argument leading to Equation (2.8) is easy because the definitions of the four units of lighting – luminous flux (lumen), illuminance (lux), luminous intensity (candela) and luminance (candela per square metre) – ensure that they tie together in a clever way. In practice, we need to calculate the light flowing from one surface to another and the reflection from the second surface to a third, and so on. To do this, one more equation is needed. If a surface scatters the light evenly, it is a perfect or ‘Lambertian’ diffuser. Its appearance is the same whatever the direction of the beam falling on it. Real surfaces are not perfect diffusers, but many of the materials of buildings can, with minor error, be treated as such. This assumption is made in much of the current software for lighting calculations. If E is the illuminance on a Lambertian surface, its luminance is L E = r p (2.9) The symbol ρ stands for the reflectance of the surface, the proportion of the light landing on it that is reflected back: if ρ = 0, the surface is perfectly black; if ρ = 1, it is a perfect white. The sky can be visualised as a diffuse plane stretching to infinity in every direction of view, or as a hemispherical dome over some point on the ground, or as a luminous gas sur- rounding us: these are equivalent in a definition of luminance. If the sky is taken to be equally bright in every direction, a useful first approximation, then there is a very simple rule linking sky luminance with illuminance on the ground: E L = p (2.10) The sky illumination on a vertical surface is exactly half that on the horizontal surface because it ‘sees’ only half a hemisphere of sky. Finally, we can use Equations (2.9) and (2.10) to find the light reflected on the façade of a building. Assume that the ground surface is diffusing (which is a good approximation unless it is wet) and that the façade looks towards open ground. Then, if the illuminance on the ground is Eh and the ground reflectance is ρg , the illuminance on a vertical surface is E E v h g = r 2 (2.11) The illuminance on the façade from both direct skylight and the light reflected from the ground, under a uniform sky of luminance Ls , would be E L L L v s s L L L g s g L ( ( ) g sky ground) = + s = 2 2 2 p p r p (2.12) Parallel beams The third of the ideal sources of light is one that gives a beam that does not diverge or converge – in technical language, a ‘collimated beam’. As a source of finite area moves away towards infinity, its apparent size decreases and its beam appears more nearly parallel. The ultimate model is a bundle of straight parallel rays such as if there were a point source at the focus of a parabolic mirror. Because the beam does not diverge, there is no change of illuminance with distance; shadows cast from the beam are crisp and non-diverging. For most lighting purposes, we can treat the sun as a source of parallel beams. It is only a small part of the sky, only one-half of a degree across in angular size, and this suggests that it should be treated as a point source. But its beam does not appear to diverge and solar illuminance seems to be unrelated to distance. The reason is, of course, that the sun is huge but a very long distance away. Distances of a few kilometres between places on the earth’s surface are negligible in comparison with the distance between earth and sun. 2.16 Parabolic mirror.
- 55. Other documents randomly have different content
- 59. The Project Gutenberg eBook of Die Welt im Kinderköpfchen
- 60. This ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online at www.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook. Title: Die Welt im Kinderköpfchen Author: Josephine Siebe Editor: Johannes Prüfer Release date: August 31, 2013 [eBook #43613] Most recently updated: October 23, 2024 Language: German Credits: Produced by Norbert H. Langkau, Iris Schröder-Gehring, and the Online Distributed Proofreading Team at http://www.pgdp.net *** START OF THE PROJECT GUTENBERG EBOOK DIE WELT IM KINDERKÖPFCHEN ***
- 61. Deutsche Elternbücherei Herausgegeben von Dr. Johannes Prüfer Heft 40 Die Welt im Kinderköpfchen Von Josephine Siebe Verlag und Druck von B. G. Teubner · Leipzig · Berlin 1919 Alle Rechte, einschließlich des Übersetzungsrechts, vorbehalten.
- 62. Frau Dr. Henriette Goldschmidt in verehrender Liebe zugeeignet
- 63. Inhalt. Seite Erste Schritte 3 Aus dem Tagebuch einer Mutter 6 Peters Reise in die weite Welt 8 Die große Verführerin 12 Hansels Liebe 17 Die Fahrt nach Schönblick 19 Pusteblumen 25 Der Brief an den lieben Gott 28 Ein Schlüssel zum Himmel 32
- 64. Einleitung. Wenn das Kind im Märchen hört, „er ging bis an das Ende der Welt“, so scheint ihm das Ziel nicht weiter erstaunlich und der Weg für einen Märchenprinzen schon ergehbar. Denn hinter Stadt, Dorf und Wald, ja vielleicht schon hinter dem Gartenzaun liegt für das kleine Kind in seiner Phantasie das Ende der Welt; nahe und doch unendlich weit, weil seinem Welterkennen immer Neues entgegentritt, mit dem es sich erst auseinandersetzen muß. Der Forschungsreisende, der nach langer Fahrt unbekanntes Land erblickt, erlebt im Grunde nichts Wunderbareres als das kleine Kind, das zum ersten Male eine Straße entlang geht, einen Garten betritt, dem sich eine bisher unbetretene Stube, eine Bodenkammer öffnet. Tut das Kind allein seine ersten Schritte und geht etwa bis zu einem Stuhl, so ist ihm der Stuhl im Augenblick Weltgrenze und Ziel. Doch weitet sich für das Kind rasch der Weltbegriff. Hinter dem Stuhl liegt die Türe, der Flur kommt, die Treppe, das Haus tut sich auf und Straße, Hof und Garten dehnen sich vor ihm, neue Gegenstände, neue Menschen treten in den Umkreis seines Blickes und jedes Wort, das es hört, jede Blume, jedes Insekt, ein Kieselstein, ein Schneckenhaus, eine Regenlache und alles was geht, kommt und fährt erweitern des Kindes Weltbild, erweitern es heute namentlich bei dem Großstadtkind mit beängstigender Schnelligkeit; doch auch das Kleinstadtkind, ja selbst das vom Lande, wenn es nicht in völlig abgelegener Gegend wohnt, lernt im Maschinenzeitalter die Welt ungleich rascher kennen als die Kinder früherer Zeiten. Zum sinnlichen Welterfassen tritt frühe auch das Streben, sich mit Gott auseinanderzusetzen; freilich, der Himmel, der sich über uns wölbt mit Sonne, Mond und Sternen, erscheint dem Kinde greifbar
- 65. nahe, und wie es oftmals begehrt, die lieben kleinen Sterne in seine Händchen zu nehmen, es den Mond verlangt und die Sonnenstrahlen fangen will, so nahe, menschlich nahe scheint ihm der liebe Gott zu sein. Der ist ihm meist der gute alte Mann, der irgendwo hinter der blauen Himmelswand sitzt, mit dem es sich abends in seinem Bettchen aussprechen kann, ja mit dem es gelegentlich auch etwas schilt wie jenes kleine Mädchen, das bei einem plötzlichen Regenguß auf die frisch geputzten Fenster weisend, mit erhobenem Fingerlein mahnte: „Na warte nur, lieber Gott, wenn das die Mama sieht.“ Der Erwachsene hat für diesen kindlichen Gottesbegriff leider oft nur ein Lächeln, wie er manchmal auch nur ein Lächeln hat für die tausendfachen Fragen der Kinder nach dem Wesen aller Dinge, für das drängende, flehende, nie verstummende Warum und doch wollen die Kleinen vom ersten Schritt in die unendliche Welt hinaus, auch wenn diese nur der nächste Stuhl ist, ernst genommen werden, verstanden sein von den großen Leuten. So ernst wie der Gelehrte, der am heiligen Born der Weisheit lauschend grübelt, oder der Forscher, der in nimmersatter Sehnsucht die Welt umschifft. Nur wenn wir versuchen, des Kindes Gedanken nachzudenken, wenn wir im Verkehr mit dem Kinde gleichsam noch einmal schon zurückgelegte Wege wiedergehen, uns des eigenen Werdens bewußt werden, dann kann es uns gelingen, einem Kinde gerecht zu werden. Wir müssen wieder mit Kindergedanken denken lernen, damit wir anscheinende Torheiten, Unsinn, ja schlimme Fehler als Entwicklungsstufen richtig werten können. In den nachfolgenden Bildern aus dem Kleinkinderleben ist versucht worden, das vielgestaltige Welterkennen des Kindes, sein Verhältnis zu seiner Umwelt, zur Natur und zu Gott in leisen Umrissen festzuhalten. Nicht als Geschichtchen aus Kindermund etwa möchten diese kleinen Schattenbilder angesehen werden, sondern als ein Beitrag zu dem großen Kapitel „Eltern und Kinder“, dem die vorliegende Elternbücherei in allen ihren Erscheinungen dienen will.
- 66. Erste Schritte. „Unser Traudchen lernt leider so schwer laufen.“ Die junge Mutter sagte dies immer ein wenig bedrückt, denn von einem Erstling verlangt doch die ganze liebe Sippe ein linschen Wunderkindtum; wenn es da mit dem Sprechen und Laufen nicht so flink gehen will, wenn Kleinchen nicht Spuren ganz ungewöhnlicher Fassungsgabe zeigt oder bedeutende Talente verrät, dann ist das für junge Eltern, namentlich wenn der Verwandtenkreis groß ist, immerhin peinlich. Und Traudchen war zwar rund und rosig, es lachte, versuchte sich auch mit wundersamen Lauten in der Redekunst, aber der kleine Ernst von Tante Elli konnte doch alles schon viel besser, und Maiers Lotte erst, die nur um zwei Tage älter als Traudchen war, erstaunlich, was die alles leistete! Überhaupt Maiers Kinder! Gegen die kam so leicht kein Kind auf, und Frau Maier füllte ihre Besuchsstunden damit aus zu erzählen, was ihre Kinder alles sagten, taten, meinten und vermutlich fühlten und dachten. Vielleicht achte ich doch nicht genug auf mein Kind, dachte Frau Irma wohl, wenn sie von der fabelhaften Entwicklung der Maierschen Kinder hörte. Und sie versuchte mit Bitten und sanfter Gewalt das schwerfällige Kind zum Laufen zu bringen. Traudchen tat dann auch ein paar schwankende ängstliche Schritte an der Mutter Hand, doch sobald diese losließ, gab es ein Zetergeschrei, und meist fiel Traudchen einfach hin, heulte und rutschte heulend zu ihrem Spielteppich zurück. Alle Künste versagten. Selbst der Vater, der einmal tatkräftig eingriff und der schwächlichen Muttererziehung
- 67. nachhelfen wollte, erreichte nichts, ja Frau Irma und Minna, das Mädchen für alles, riefen, so jämmerlich habe Traudchen noch nie geschrien. Der Arzt erklärte Traudchen dabei für ein völlig normales gesundes Kind, er riet zur Geduld und redete lächelnd von Erstlingssorgen. Ach Geduld, wenn man sein Kindchen doch etwas bewundert sehen möchte und heimlich, trotz aller Versicherungen des Arztes, doch die Angst im Herzen trägt, vielleicht ist das Kindchen nicht ganz gesund, vielleicht bleibt es zurück im Wachstum an Körper und Geist. Was man für Sorgen hat um so ein Kindchen! „Man muß es mit Lockmitteln versuchen“, erklärte der Vater. Und er ging hin und kaufte als erstes Lockmittel einen bunten Hampelmann, nach dem Traudchen kreischend griff. Zwei Minuten durfte es damit spielen, dann wurde der Hampelmann an der Tür befestigt und der Vater rief: „Komm Traudchen, komm, sieh Hampelmann!“ „Dada!“ Traudchen griff mit den Händchen in die Luft, stellte sich mit Hilfe der Mutter auf ihre Beinchen, doch als die losließ, gab es das übliche Zetergeschrei. Plumps! saß Traudchen und darüber vergaß es den Hampelmann. Am nächsten Tag versuchte der Vater es mit einem schwingenden Ball, den löste ein Holzpapagei ab, ein schnurrender Blechhahn folgte und jedesmal gab es den gleichen Verlauf. Traudchen freute sich, griff danach, versuchte auch das Gehen, schrie und versuchte schließlich kriechend ihr Ziel zu erreichen. Und immer wieder die Frage: „Kann Traudchen noch nicht laufen?“ — „Nein, immer noch nicht!“ Eines Tages kam Frau Maier, die Mutter der vortrefflichen Kinder, sie kam von einem Einkaufsgang, und da sie sich nicht allein als besondere Mutter, sondern auch als besondere Hausfrau fühlte,
- 68. kaufte sie immer besonders billig, und nachdem sie ihr Erstaunen über Traudchens Nichtlaufenkönnen wortreich geäußert hatte, fing sie an, ihre Einkäufe zu zeigen. Sie hatte im Warenhaus allerlei Tand erstanden, für den sie Bewunderung heischte. Darunter war auch ein kleiner feuerroter Milchtopf, der bei dem Auskramen seine Umhüllung verlor, Frau Maier stellte ihn etwas achtlos neben sich auf einen Hocker und vergaß ihn über den vielerlei weisen Reden, die zu halten sie sich verpflichtet fühlte. Da stand das Töpfchen und die Sonne blinkerte auf ihm herum, vielleicht weil sie nichts anderes zu tun hatte. Denn ein besonderes schönes Töpfchen war das kleine feuerrote Jahrmarktdings gerade nicht, keins, das auf Ausstellungen oder in einen Glasschrank gehört, aber dem Traudchen gefiel es. „Dada!“ jauchzte es und patschte in die Hände. Dada hatte vielerlei Bedeutung. Die Mutter sah auf, doch da Traudchen ganz vergnügt an einem Stuhlbein herumkletterte und Frau Maier kein Päuslein in ihrem Redefluß eintreten ließ, achtete sie nicht weiter auf die Kleine. „Dada!“ Traudchens Hände griffen in die Luft und ihre Blicke hingen wie gebannt an dem roten Töpfchen. Wenn's nur nicht so weit gewesen wäre! Traudchen stand auf einmal auf seinen zwei Beinchen und niemand sah es. Und die Kleine vergaß das haltgebende Stuhlbein, ihr Eifer, zu dem roten seltsamen Dings zu gelangen, war zu groß. Ein Schrittchen tat es in die grenzenlose Weite der Stube hinein, noch einen. „Mein Gott, sehen Sie!“ Frau Irma ließ Frau Maier nicht Zeit, das notwendige Gewürz unter den Kuchen zu mischen, dessen geheimnisvolle Zubereitung sie gerade verraten wollte, „sehen Sie doch, unser Traudchen läuft. Fritz, Fritz, Minna kommt schnell herein, Traudchen läuft!“
- 69. Doch ehe die Gerufenen anlangten, hatte Traudchen schon ihr Ziel erreicht und — es klirrte, platsch lag das rote Töpfchen auf dem Boden. „Dada!“ Traudchen sah sich nicht ohne einen gewissen Stolz über das vollbrachte Werk um. „Dada“, sie griff nach einem geheimnisvollen Päckchen, was Frau Maier auch auf den Hocker gelegt hatte, doch die kam ihr zuvor und mit dem entrüsteten Ruf: „mein schönes Milchkännchen“, entriß sie Traudchen den neuen Raub. „Traudchen läuft, da vom Stuhl bis hierher ist sie gelaufen!“ Der Vater und Minna bekamen beide das Wunder verkündet und Traudchen platschte mit ihren Händchen auf den Hocker und kreischte vor Lust. Frau Maier lächelte sauersüß. Nein, so hatte sie sich mit ihren Kindern wirklich nicht angestellt, und nicht einmal ein Wort der Entschuldigung sagten die Eltern. Sie stand auf und erklärte, sie müßte gehen. „Ist es nicht entzückend, wie sicher das Kind gegangen ist?“ Frau Irma strahlte. Sie schob mit dem Fuß ein wenig die Scherben beiseite und sagte gleichmütig: „Morgen bringe ich Ihnen einen andern Topf, liebe Frau Maier. Im Warenhaus gibt es ja noch so viele.“ Frau Maier kam gar nicht dazu, eine höfliche Abwehr zu sagen, denn der junge Vater rief eifrig, man müßte etliche von diesen Töpfen holen, denn es sei immerhin erstaunlich, warum das Kind es gerade darauf abgesehen hätte und man müßte untersuchen, ob Farbe oder Form den Anreiz gegeben hätten. Frau Irma war das gleichgültig. Sie dachte nur: mein Kindchen läuft, Gott sei Dank, es hat keinen verborgenen Fehler.
- 70. Und nach zwei Jahren klagte die junge Mutter: „Unser Traudchen ist ein Quirl. Nicht zehn Minuten sitzt das Kind still, heute ist es wieder heimlich auf die Straße gelaufen, wenn es nur nicht so eine Range wird wie Maiers Kinder.“ Die Sorgen nehmen halt kein Ende!
- 71. Aus dem Tagebuch einer Mutter. Wirklich, ich bin keine eingebildete Mutter. Ich finde zwar meinen Erstgeborenen über die Maßen lieblich, doch das finden andere auch, die beiden Großmütter zum Beispiel, aber ich erkenne doch an, daß es noch andere nette Kinder gibt. Wenn freilich mein kleiner Schelm so seinen blonden Kopf an meine Brust lehnt und mich mit seinen dunklen Augen anstrahlt, dann — ja dann erscheint er mir eben wie ein kleiner Engel. Doch ganz engelhaft ist er nicht immer. Leider. Er hat einen Dickkopf. Sein Vater sagt, den hat er von mir, ich sage, darin gleicht er ihm. Neulich kam Tante Berta gerade dazu, als Mutter und Sohn über das Spazierengehen anderer Meinung waren. Etwas laut ging es zu. Das kann ich nicht leugnen. Das Söhnlein trampelte und schrie, die Mutter schalt und weinte. Nein, engelhaft war es wohl nicht. Doch abscheulichen Trotzkopf brauchte Tante Berta den Buben auch nicht zu nennen. Das war zu viel. Wenn Bubi nur weniger geschrien hätte! Zum Davonlaufen war es wirklich und Tante Berta lief auch davon. Ich begleitete sie hinaus, ein bißchen heiß und aufgeregt und just da kam unsere Hausgenossin, die Hofrätin, die Treppe hinauf. Sie sah meine Tränen, hörte Tante Bertas Ermahnungen, strenger zu sein, und da klagte ich ihr meine Not. Da strich mir die liebe alte Frau sacht über das heiße Gesicht und sagte sanft: „Ruhe und Geduld braucht es zum Muttersein. Kind, mit
- 72. Heftigkeit in Strenge und Liebe richtet man wenig aus.“ „Ich würde den Bengel tüchtig verwichsen“, rief Tante Berta, die mit festem Schritt die Stiege abwärts ging. Wer hatte nun recht? Still kehrte ich zu meinem kleinen Unband zurück. Mit verheultem Gesichtchen saß er in seiner Ecke und knurrte: „Will nicht spazieren gehen, will nicht gehen!“ Ich schwieg. „Ruhe und Geduld“ klang's in mir nach. Zwang ich ihn jetzt, begann wohl das Geschrei von neuem. Ich setzte mich also an meinen Schreibtisch und begann meine Wirtschaftsrechnung. Auf einmal kam aus Bubis Ecke ein Seufzerlein. Ich rechnete weiter — wieder ein Seufzer! Nun war er still, dann klang es zaghaft: „Mutti!“ Mein Kopf machte eine halbe Wendung. Nein noch war es nicht Zeit. Ich rechnete krampfhaft 15 und 37 sind 74 — oh welche närrischen Summen kamen heraus! Wieder ein Seufzerlein. Es raschelte. Trapp trapp kam's daher, und dann huschelte es sich weich und warm an mich an und flehend und ach so kläglich klang es: „Mutti — Mutti!“ Rasch wollte ich den lieben unnützen Schelm an mich ziehen und ihn tüchtig abküssen, als mir der alten Frau Mahnung einfiel: „Mit Heftigkeit in Strenge und Liebe richtet man wenig aus.“ Ich streichelte also nur linde meinen Trotzkopf und fragte gelassen: „Warum hast du denn keine Lust zum Spazierengehen?“ „Weil — weil ich doch in der Eisenbahn saßte und weil ich doch Schaffner war und weil — weil ich doch nach Berlin fahrte!“
- 73. Also im Spiel hatte ich ihn gestört, das war's. Herausgerissen aus seinem heiteren bunten Phantasieland hatte ich ihn. Ich sagte ganz ernsthaft: „Schau, Bubi, nun bist du doch einmal ausgestiegen, da kannst du ja auch spazieren gehen. Wenn du heimkommst, fährst du dann weiter!“ — „Hm!“ „Marie, bringen Sie Bubis Mantel, wir gehen jetzt spazieren.“ Und er ging mit. Erst etwas mürrisch, dann so froh wie immer. Mein — ich muß es leider gestehen — erster Sieg. Doch ich hoffe mehr zu erringen. Ruhe und Geduld, ich will immer daran denken und auch daran, meinen Buben nicht zu rasch aus seinem Spiel zu reißen. Ich werde ja selbst ärgerlich, wenn man mich gedankenlos in meiner Arbeit stört, und dem Kinde ist das Spiel Arbeit, Betätigung, für die es ganz unbewußt von den Erwachsenen Verständnis fordert. Was ist das, Bubi schreit nebenan! Ganz aufgeregt klingt seine Stimme. „Marie, Marie, Sie gehen ins Wasser.“ — „Ih nee!“ brummt Marie und schlurft aus dem Zimmer. Ich gehe hinüber. Da sitzt Bubi auf einem Kissen auf dem Fußboden und ruft mir glückselig zu: „Ich bin Schiff, Mutti, fall nicht ins Wasser!“ Nein, ich will nicht in das rinnende klare Traumwässerlein treten, auf dem er so selig dahinfährt, wie der Schiffer auf dem blauen Meer der Insel des Glücks zuschifft.
- 74. Peters Reise in die weite Welt. Wenn ein kleiner Peter Höslein trägt mit Taschen darin und vier Jahre alt ist, dann kann er schon in die weite Welt reisen. Nur die Unvernunft der großen Leute sieht das nicht ein. Ach, die großen Leute! Man hat es manchmal schwer mit ihnen, wenn man selbst noch nicht zu ihnen gehört. Da sagt zum Beispiel der Vater an einem schönen lichten Sommertag ganz ungewöhnlich streng: „Peterle, wenn du wieder wie gestern die Kaninchen aus dem Stall läßt, dann gibt es Haue, merke es dir!“ Peter hat heute gar nicht an die Kaninchen gedacht, aber nun läuft er schnell zum Stall, natürlich nur, um den Kaninchen ihr Schicksal zu verkünden. Er redet mit den geliebten Schnupperchens und denkt nicht daran, die kleine Stalltüre zu öffnen. Bewahre. Wenn nur das weiße Kaninchen, sein besonderer Liebling, nicht so eindringlich bitten möchte. Peter nimmt dies beharrliche Am-Gitter- Sitzen für eine sehr flehende Bitte, und er redet dem Weißling betrübt zu: „Mußt drin bleiben!“ Aber da hopst ein gelbes heran, auch ein schwarzes nähert sich, alle sehen Peter so bittend an, und auf einmal, Peter weiß selbst nicht, wie es geschehen konnte, ist das Türlein auf, und husch, husch! laufen die Kaninchen in den Garten, in den schönen gepflegten Garten. Wer soll sie nun wieder einfangen? Peter weiß gleich, das kann er nicht. Vorgestern hat er die Ausreißer heulend gejagt, aber keines ergriffen, und dazu fällt ihm
- 75. noch des Vaters Drohung ein. Und Vater spaßt nicht. Peter rennt durch den Garten, dahin, dorthin. Dabei kommt er an das Ausgangstor, ein Spältchen steht es auf, man kann gut hinausschlüpfen. Ausreißen, wie die Kaninchen ausgerissen sind, in die weite Welt hinauslaufen! Peter denkt es nicht, er fühlt es nur halb unbewußt, und plötzlich steht er draußen auf der Straße. Zum erstenmal allein. Peterle ist ein wohlbehütetes Kind, immer geht er sonst nur mit den Eltern oder mit Fräulein spazieren und immer nur in den Gängen des nahen Parkes, er kennt nur die Straße, in der seines Vaters Villa liegt, und die nachbarliche, in der die Großeltern wohnen, nicht jene Straßen, in denen die Häuser dicht gedrängt stehen, himmelhoch aufgebaut. Und doch braucht man nur ein paar Schritte zu gehen, und schon läuft so eine lange Häuserzeile dahin, eine Straße voll Leben. Wagen fahren, Menschen hasten sie entlang und Kinder spielen auf ihr, immer zu jeder Tageszeit, viele, viele Kinder. So viele Kinder hat Peter noch gar nicht gesehen. Wenn nun einer in die weite Welt reisen will und nicht fahren kann, dann muß er laufen, und Peterle läuft, ein bißchen Angst, erwischt zu werden, ist auch dabei, also rennt er trapp trapp die Straße entlang, und so eilig hat er es, daß er eine dumme Bordschwelle nicht sieht, er stolpert und pardauz! gibt es den ersten Aufenthalt auf der Reise in die weite Welt hinaus. Wenn Peter daheim fällt, dann heult er, bis man ihn aufhebt, ihn tröstet, ihm einen Leckerbissen verspricht, und darum heult er jetzt auch, heult jämmerlich, aber — es hebt ihn niemand auf. Nur eine dünne schrille Stimme schreit ihn an: „Biste gefall'n?“ Es ist, als ob diese Stimme den Kleinen in die Höhe zieht, er steht auf und sieht sich höchst verwundert um, da steht ein Mädel, etwas größer als er, die sieht ihn spöttisch an und fragt höhnisch: „Haste dich dreckig gemacht?“
- 76. Daß die weißen Höslein schmutzig sind, bekümmert Peter nicht weiter, denn daheim liegen noch viele saubere weiße Höslein, er sieht nur die Fragerin, wie ein Weltwunder starrt er sie an. Sie trägt ein verschlissenes Kleid, im schwarzen Wuschelkopf brennt ein rotes Bändchen und in den festen braunen Händchen hält sie eine unglaublich dicke Schnitte, deren Musbelag seine Spuren dem ganzen Gesichtchen aufgedrückt hat. „Willste mal beißen?“ Peter ißt zu Hause nicht alles, was man ihm reicht, aber in die dicke Schnitte beißt er herzhaft hinein, und während er kaut und schluckt und auch ein Musbärtlein bekommt, sagt die Spenderin: „Ich heiße Mine, wie heiste denn?“ Peter gurgelt seinen Namen heraus, und die Freundschaft ist geschlossen. Mine pflegt schnell Freundschaften zu schließen, und weil weder Guste noch Marie, Liese, Otto, Fritze und Paul just auf der Straße sind, um mit ihr zu spielen, kommt ihr der kleine Weltreisende gerade recht. Sie fragt: „Wo kommste denn her?“ Peter weiß nicht, wo seines Vaters Haus liegt, er ahnt aber dumpf, Mine würde Verständnis haben für seine Reise in die weite Welt. Er erzählt. Nicht ganz so zungenschnell, wie Mine redet, aber die versteht ihn gut, sie nickt und antwortet beifällig: „Wenn ich Haue kriegen soll, reiß ich immer aus. Vater haut so sehr. Woll'n mer Himmel und Hölle spielen?“ Peter kennt das Spiel nicht, und Mine nennt ihn ohne viel Umstände dumm, sie sieht ihn etwas verächtlich an, aber sein weißer Anzug, seine wohlgepflegte Niedlichkeit versöhnen sie doch wieder, und sie nimmt den kleinen Ausreißer gnädig als Lehrling an. Und dann kommen Guste und Marie, Fritz und Paul gesellen sich dazu, und alle blicken halb mißtrauisch, halb verlegen den „feinen Neuen“ an. Doch Mine erklärt, und das Zauberwort: „Er ist ausgerissen“ befördert das Vertrauen; Peter darf mittun.
- 77. Sie spielen auf der Straße. Peter hat es noch nicht geahnt, welche wunderbaren Spiele es gibt. Himmel und Hölle ist bald abgetan, Feuerwehr wird gespielt und Schutzmann. Paul mimt zur johlenden Freude der anderen einen Betrunkenen, so wie gestern einer auf der Straße herumgetorkelt ist. Er schimpft wie der Betrunkene, stößt Worte aus, die Peter noch nie gehört hat, aber die er sich flinker merkt als die Verslein in seinen Bilderbüchern, die Fräulein ihm manchmal vorsagt. Fritz ist ein sehr schneidiger Schutzmann, die Mädels kreischen, und Peter kreischt mit. Er findet das Spiel so köstlich wie noch keins zuvor, und er vergißt darüber den Garten, die entlaufenen Kaninchen, alles; er ist draußen in der weiten, unbekannten Welt, und er genießt sein erstes Abenteuer mit vollen Zügen. — In Peters Elternhaus ist die Sorge wach geworden. Fräulein hat des Kleinen Verschwinden zuerst entdeckt. Sie meint, er habe sich versteckt, und sie sucht ihn, erst lässig mal seinen Namen rufend, dann besorgter, aufgeregter; sie läuft mit ihrer Angst zu den anderen Hausbewohnern und zuletzt sind alle auf der Suche nach dem Ausreißer. Sie rennen auf die Straße, fragen da und dort, niemand hat Peter gesehen, und die Mutter weint verzweifelt; sie sieht ihr Kind bereits überfahren, verschleppt, sie ruft nach ihrem Mann, nach der Polizei. Der Fernsprecher klingelt, und als die Aufregung auf das höchste gestiegen ist, erscheint Fräulein mit dem heulenden widerborstigen Peter. Er sieht schmutzig und erhitzt aus, daß er seine Weltreise so schnell aufgeben mußte, bereitet ihm offenbar wenig Vergnügen. Mit Straßenkindern hat er gespielt. Unglaublich! Die Mutter ist entsetzt, Fräulein ist entsetzt, und die Mädchen stellen sich an, als wäre ein goldenes Krönlein in einen tiefen Brunnen gefallen.
- 78. Der Vater lacht. Doch er ist ein Mann der Tat und vergißt nicht, sein väterliches Wort einzulösen. Diesmal hilft kein Bitten der Mutter, nicht Fräuleins Tränenströme. Vater und Sohn reden eindringlich und recht unangenehm miteinander, und zuletzt sagt der Vater stolz auf seine Erziehungskunst: „So, das Ausreißen habe ich ihm gründlich ausgetrieben.“ Nach drei Tagen ist Peter wieder verschwunden. Diesmal ist es kein unbewußtes Hineintappen in die weite Welt mehr, heimlich und bedacht ist er entschlüpft; denn die Straße mit Mine und ihren Spielgenossen erscheint ihm lockender als der große, stille Garten; in ihm brennt die Sehnsucht, einer unter anderen zu sein. Fräulein hat die Flucht entdeckt, und sie holt ihn diesmal zurück, ohne erst das Haus zusammenzuschreien, nur der Mutter wird der neue Streich verraten, und die beiden Frauen reden eindringlich auf Peter ein; seine Sünde wird ihm wortreich vorgehalten, und als die Mutter meint, es sei genug, redet Fräulein noch weiter. Peter schielt sie bockig an, und auf einmal sagt der wohlerzogene kleine Junge, der nach seiner Eltern Willen aufwachsen soll, behütet von allem Häßlichen, Unreinen der Welt, trotzig zu Fräulein: „Du Luder!“ So sagt Mine, und Mine ist für ihn Lust, Spiel, Lachen; sie ist ihm das bunte, wechselreiche Leben, und was Mine sagt, ist fein, hat Geltung für ihn. Am nächsten Tag versucht Peter es wieder, auszureißen. Die Sehnsucht nach dem Draußen, nach den andern verläßt ihn nicht mehr.
- 79. Die große Verführerin. „Mutti, dürfen wir auf die Straße?“ Das Trüpplein steht vor der Mutter, die Augen glänzen unternehmungslustig, sie hoffen auf ein Ja, und die Mutter sagt es auch, sie sagt es freilich ungern und zögernd, es ist ihr gar nicht recht, wenn die Kinder allein spielen. Doch, um sie spazieren zu führen, dazu fehlt es ihr an der Zeit, und die drei lebhaften Dinglein immer in der engen Wohnung zu lassen und ihnen kein Draußensein zu erlauben, geht doch auch nicht an. Luft und Sonne, sie brauchen beide so nötig. Doch der Mutter ist die Straße unheimlich, ihre Flurnachbarin hat gesagt: „Das sind Kleinstadtgewohnheiten, die muß man überwinden. Wer nicht mit 'nem goldenen Löffel in der Hand geboren ist, der darf sich heute nicht absperren. Meine Kinder sind immerzu auf der Straße, da werden sie dreist und umgänglich und kommen nachher gut fort im Leben.“ Gut fortkommen im Leben, es leichter haben als ich sollen meine Kinder auch, denkt Frau Anna. Um ihretwillen ist sie ja weggezogen aus der lieben kleinen Heimatstadt, auf deren Plätzen noch die Brunnen rauschen wie in einem Eichendorffschen Liede. Kluge Ratgeber haben gemeint, sie würde in der Großstadt bessere Arbeitsgelegenheiten haben, und sie ist dem Rat gefolgt und hat wirklich die erhoffte Arbeit gefunden, nun sitzt sie von früh bis abends an der Maschine und stickt mit farbiger Seide feine schöne Blumen und Muster auf köstliche Stoffe. Dem Prunk und heiterem Glanze dient die Arbeit ihres einsamen Lebens. Ihr Mann ist tot und
- 80. die Sorge für ihre drei Kinder ruht auf ihr. Eine schwere Sorge, ja, und doch eine liebe Sorge. Frau Anna hört die Flurtüre klappen, jetzt trappeln ihre drei die Treppen hinab, und der große Bruder, der nun bald ein Schulrekrut ist, beschützt sorgsam die kleinen Schwestern, so wie er es daheim schon tat. Wenn nur die Straße, der sie zustreben, auch jener der verlassenen Heimat gleichen möchte: Da hatten sich Gärten zwischen die Häuser geschoben und die Bäume hatten im Frühling ihre Blüten, im Sommer und Herbst wohl auch einen Teil ihrer Früchte auf die Straße niederfallen lassen, zum Ärger ihrer Besitzer, zur Freude der Kinder. Die Maschine klappert, Stich um Stich. Frau Anna stickt verschlungene Linien auf blauen Grund; wer der Linien Anfang und Ende nicht kennt, hält das Ganze wohl für ein regelloses Gewirr, und doch ist es ein Muster, schön und geheimnisvoll, schwer zu enträtseln freilich, wie manchmal des Lebens Gang. Die Zeit vergeht. Frau Anna sieht nach der Uhr und erschrickt, die Kinder bleiben doch so lange aus. Sie wird unruhig und wartet, und die Arbeit schreitet langsamer voran. Da endlich krabbelt es draußen an der Flurtüre, ein zaghaftes Klingeln ertönt. Das ist doch nicht der Seppel, der klingelt immer herzhafter, vom Stuhl kann man fallen vor Schreck, wenn der Einlaß begehrt. Frau Anna geht und öffnet und sie findet draußen Ruth und Trinchen stehen, und allen beiden laufen die Tränen über die Bäckchen. „Seppel ist fortgelaufen“, klagt Ruth, und das Trinchen jammert: „Fottelaufen!“ Seppel hat die Schwestern allein gelassen! Zum erstenmal tat er das. Frau Anna denkt nur an ein Unglück, das geschehen sein muß, und sie bringt es kaum noch fertig, die etwas redselige, aber immer hilfsbereite Nachbarin um Schutz für ihre beiden Kleinen zu bitten,
- 81. dann rennt sie eilig die Treppe hinab, ihren Jungen zu suchen, ihren Liebling. Wo ist er, was ist ihm begegnet? Sie braucht nicht weit zu gehen, da findet sie ihn schon. Er steht mitten unter einer Schar von Buben, der Kleinste ist er unter ihnen, aber sein Stimmlein kräht doch laut im Chore mit. „Seppel!“ Als die Mutter ihn ruft, schrickt er zusammen, er blinkert verlegen mit den Augen, denn leise dämmert der Gedanke an die verlassenen Schwestern in ihm auf. Unsicher murmelt er: „Sie sind weggelaufen.“ „Nein, du bist weggelaufen!“ Frau Anna sagt es ganz ruhig, und ein heimliches Lachen kommt ihr, als sie in Seppels bedrücktes Gesichtlein sieht, sie straft ihn aber doch mit Worten, wenn sie auch milde sind, und schon auf der zweiten Stiege stammelt der Kleine reumütig die Bitte um Verzeihung, sagt, er will's nicht wiedertun. Das Versprechen kommt aus ehrlichem Herzen, und die Mutter atmet auf, als sie ihre drei wieder beisammen hat. Am nächsten Tag gelobt Seppel feierlich, die Schwestern treu zu hüten, und sie kommen auch alle drei vereint wieder zurück, ein bißchen verheult sieht das Trinchen aus, es ist hingefallen, weil die beiden Großen zu schnell gelaufen sind. Der Feuerwehr nach. Was kommt alles auf so einer Straße daher, was zum Nachrennen verlockt! Besonders so einen kleinen, kecken Draufgänger, wie der Seppel ist, einen, der einem dummen Streich nicht immer ausweicht und dem sich leicht ein Geschehen im Bewußtsein vergrößert und verschiebt, weil seine bewegliche Phantasie alles zu einem besonderen Erleben gestaltet. Wenn die Kinder zurückkommen, haben sie immer viel zu berichten, sie nennen auch Namen von anderen Kindern, und manchmal fallen Worte, bei denen die Mutter erschreckt aufhorcht
- 82. und mahnt, das sagt man nicht und dies nicht. Nur das Trinchen hat immer weinerlich das gleiche Erlebnis zu beklagen. „Bin defall'n.“ Frau Anna merkt es, das Trinchen kommt bei dem Auf-der-Straße- Spielen zu kurz, und an einem Tage, der warm und sonnenreich ist, als wäre es schon Frühling, verläßt sie die Arbeit und geht ihren Kindern nach, um zu sehen, mit wem sie unten spielen. Als Frau Anna die Straße betritt, erschrickt sie vor ihr. Der warme Tag hat mehr Menschen als sonst herausgelockt, und die Straße ist ganz erfüllt von brausendem Leben, ihr, der Kleinstädterin, erscheint es ungeheuer, und doch rechnet der Einheimische diese Straße zu den stilleren der Stadt. Die Mutter schaut ängstlich nach ihren Dreien aus, und übersieht dabei beinahe das Trinchen, das auf der Bordschwelle zwischen Bürgersteig und Fahrdamm sitzt, ganz allein hockt es da und haut mit einem alten Blechlöffel immer auf das Pflaster und summt vor sich hin: „Bumsa, bumsa!“ Die Puppe liegt daneben, und inmitten alles Lebens erscheint der Mutter ihr Kleinchen so unsäglich verlassen, daß ihr die Tränen kommen. Sie hebt es auf, und Trinchen jauchzt laut beim Anblick der Mutter, aber gleich klagt es wieder, wie so oft: „Bin defall'n.“ Nach Ruth braucht Frau Anna nicht weit zu suchen, die kommt bald angerannt, will nach dem Schwesterchen sehen und erzählt strahlend, sie hätten Haschens gespielt, aber das Trinchen könne noch nicht so geschwind laufen. Und Seppel? Der spielte mit den großen Jungen Krieg, er hatte die Schwestern wieder vergessen, und als die Mutter suchend die Straße entlang geht und eine ganze Schar Buben daherstürmen sieht, begreift sie es, Seppel ist eben ein Junge, er will sich austoben. Diesmal ist Seppel auch gar nicht reumütig, ja er brummt, als die Mutter ihn ruft, und er setzt das Brummen oben fort; denn er kommt sich ein wenig wie gefangen im Käfig vor.
- 83. Am nächsten Tag hat sich der vorzeitige Frühlingsglanz in Regen verwandelt, und auf Frau Annas Herz ist eine neue Sorge gesunken, Trinchen fiebert und liegt im Bett. Die Nachbarin holt bereitwillig den Arzt herbei, der kommt auch und beruhigt die Mutter, es wäre nicht schlimm. Dennoch wagt sich Frau Anna von der Kleinen nicht fort, und da die Nachbarin keine Zeit hat, schickt sie Seppel nachmittags auf die Straße, er soll allerlei einholen. Sein Wiederkommen dauert sehr lange, und als er endlich kommt, tanzt die Klingel nicht so lebhaft wie sonst, nur zaghaft tönt sie, und Seppel kommt sehr bedrückt in das Zimmer, und sein Blick weicht scheu dem der Mutter aus. Was bedrückt ihn denn? Frau Anna prüft das Eingeholte, es ist alles da, nur das Geld, das Seppel zurückbringen soll, fehlt. Er hat es verloren. Noch während er das Wort ausspricht, kommen ihm die Tränen; er heult laut und erklärt schluchzend, man hätte es ihm fortgenommen. „Wer denn?“ Seppel schweigt. Im Mundwinkel und am Kinn sieht die Mutter zwei verdächtige braune Fleckchen, und sie frägt und forscht, und da kommt es denn heraus, zwei Freunde von der Straße, zwei größere Jungen, haben Seppel das Geld fortgenommen und es in Näschereien angelegt, ihm haben sie ein Beuteteilchen davon abgegeben und den guten Rat dazu, das Märlein vom verlorenen Gelde zu sagen. — In dieser Nacht findet Frau Anna keine Ruhe. Sie sitzt an Trinchens Bett und hört den Atem des Kindes ein wenig unruhig gehen. Nebenan in der Kammer schlafen Ruth und Seppel tief und fest. Der Bube ist unter Tränen eingeschlafen, und als die Mutter einmal zu ihm geht, sieht sie ein Lächeln auf seinem Gesichtchen kommen und gehen, seine Schulderkenntnis ist noch nicht so tief, um ihm den Schlaf zu stören, noch spürt er nicht, wo sich die Wege senken, die in die Tiefe führen.
- 84. Frau Anna geht ruhelos zwischen Kammer und Stube einher. Trinchen schläft jetzt ganz ruhig, und sie tritt an das Fenster und sieht auf die Straße hinab. Es hat geregnet und die Lichter spiegeln sich auf dem feuchten Pflaster. Die Fenster gleichen alle geschlossenen toten Augen, nur zwei glänzen noch hell in die Nacht hinaus. Und Frau Anna denkt, wer ist es, der dort noch wacht, vielleicht auch eine Mutter in Sorge wie ich? Da hallen Schritte unten. Ein paar Männer reden laut, Frauenstimmen mischen sich hinein und ein häßliches kreischendes Lachen schallt auf. Dann verlieren sich Schritte und Stimmen in der Ferne, nur der häßliche Nachklang bleibt Frau Anna noch im Ohr. Und ein Grauen packt sie vor der langen dunklen Straße da unten, der großen Verführerin. Was verhüllt und verbirgt sie alles, was erblickt der Wissende und hört der Hörende, wenn er sie entlang geht? Wieviel Jugend, wieviel lachender Leichtsinn fiel ihr schon zum Opfer! Da tönt nebenan ein leises Rufen auf und rasch tritt sie zurück und geht wieder zu ihren Kindern. Seppel sitzt aufrecht im Bett und als die Mutter in den Lichtschein der Lampe tritt, blinzelt er schlaftrunken. „Durst, Mutti“, murmelt er. Frau Anna läßt ihn trinken. Er schluckt ein paarmal, zuletzt schon mit geschlossenen Augen, dann sinkt er zurück, greift noch tastend nach der Mutter Hand und ein ganz holdes Lächeln geht über sein Gesichtchen. Mutti! Da ist er wieder eingeschlafen und vielleicht tummelt er sich nun schon auf der allerbuntesten Traumwiese herum. Der Mutter Hand aber hält er fest, und aus dieser kleinen Hand scheint der Frau ein Kraftstrom zuzufließen. Ihr Herz schlägt ruhiger, still sitzt sie im warmen Schein der Lampe, draußen liegt die Straße im Dunkel, aber innen ist Licht und Leben. Liebes junges Leben, das ihr gehört. Wird sie es schützen können gegen die Welt draußen?
- 85. Sie lächelt tapfer. Meine Kinder, denkt sie, meine Kinder, und es ist ihr als fühle sie ihre Stärke wachsen. Riesenkraft kann eine Mutter haben.
- 86. Hansels Liebe. Elf Tanten und vier Onkels, alle sollte Hansel lieben, und er stopfte sie auch wirklich alle in sein Herzelein hinein, so gut es ging, er spendete Patschhände und freundliche Blicke, er ließ sich auch mal küssen, doch glücklicherweise nicht allzugern. Und wenn die Tanten gar zu lange bei seiner Mutter blieben, war er höflich und öffnete die Flurtüre und rief in das Zimmer hinein: „Ich habe schon die Türe aufgemacht.“ Machte er Pläne für künftige Lebenszeiten, er schwankte, ob er Kutscher, General oder Schutzmann werden sollte, dann brachte er auch da und dort einen Onkel oder einige Tanten unter, von letzteren versprach er etlichen die Ehe und einen Onkel ernannte er schon zu seinem Trompeter, im Fall er das Generalsein erwählte. Die Tanten waren mitunter ein bißchen eifersüchtig gegenseitig auf Hansels Liebe, obgleich der Kleine seine Gunst ziemlich gerecht verteilte und die Schokolade von Tante Anna genau so gern aß wie die von Tante Ida, sie hätten aber alle gern in seinem kleinen Herzen auf dem Sofa neben Vater und Mutter gesessen, aber der Platz gehörte für einige Zeit jemand, der gar nichts davon ahnte. Am eifersüchtigsten warb Tante Ida um Hansels Liebe; mit süßen Gaben, mit Spaß und Neckerei suchte sie das kleine Herz an sich zu fesseln, es gehörte ihr auch, bis die seltsame Nebenbuhlerin kam. Ein Vorfrühlingstag war es. Ein rauhes Lüftlein wehte, und Tante Ida strebte mit Hansel heimwärts, sie fand, es sei Zeit, und sie war der Ansicht, ihr Tantenamt gut erfüllt zu haben. Eine
- 87. Trillerpfeife — seine höchste Sehnsucht zur Zeit — steckte in seiner Tasche, ein Küchlein ruhte auf dem Grunde seines Magens, und immer hatte Tante Ida vorsichtig die Sonnenseite aufgesucht. Und auf einmal walzte sie daher: „Hansels Liebe“. Die Straße zitterte und dröhnte, schwarz, ungeheuer, fauchend kam sie angekeucht, die Dampfwalze. Hansel stand wie angewurzelt. „Komm“, mahnte die Tante, „komm!“ Hansel rührte sich nicht. Seine Augen ruhten unverwandt auf ihr, der Herrlichen. Was war selbst die Elektrische gegen sie! Die Tante bat und mahnte, es half alles nichts. Hansel rührte sich nicht von der Stelle. Endlich rief die Tante, der es kühl um die Ohren wehte, ärgerlich: „Ich glaube wirklich, Hansel, du hast die Dampfwalze lieber als mich.“ Und Hansel drehte sich um, sah die Tante liebenswürdig mit seinen strahlenden Braunaugen an und sagte tröstend: „Nur ein bißchen, Tante.“ Vergessen waren alle Liebesbeweise, die Dampfwalze hatte gesiegt. Wer kennt sich aus in einem Kinderherzen! Hansel, der inzwischen ein Hans geworden ist, will Ingenieur werden. Wenn er das Dröhnen und Rasseln der Maschinen hört, wenn die Bahnen sausen, die Kraftwagen surren, wenn er den gewaltigen Rhythmus der Arbeit spürt, dann zuckt sein Herz in tiefer Freude, weil er ein Mitschaffender sein kann, und er lauscht dem Zusammenklingen der vielen Stimmen so hingegeben wie damals, als er die Dampfwalze erblickte.
- 88. Die Fahrt nach Schönblick. Einmal, so um die Sommerferienzeit, sagte der neunjährige Hellmut beim Mittagessen: „Kirchners verreisen; Max sagt, er kann dann auf 'nem richtigen Schiff fahren, immer, alle Tage.“ Die zehnjährige Else bekommt unruhige, erwartungsvolle Augen, und Sehnsucht schwingt in ihrer Stimme, als sie erzählt: „Bei uns in der Klasse reisen fast alle.“ In dem blassen Gesicht der Mutter zuckt es, sie sieht an ihrem Mann vorbei; denn sie weiß genau, der denkt jetzt: Könnte ich doch mit euch auch eine Ferienreise machen, einmal ein paar Wochen lang im Walde leben. Im Wald, den er so liebt, er, der Förstersohn. Wenn nur nicht alles so teuer wäre, wenn man nur einmal etwas sorgloser dem Tage leben könnte! Weil die Eltern schweigen, verebbt das Gespräch. Den beiden Kleinen, die mit ihren fünf und drei Jahren ohnehin noch keine Reisesehnsucht kennen, ist es gleich, ob eine oder zehn Klassen reisen, und Ferdel schwatzt lustig dazwischen, und die sinnige Marie freut sich an den bunten Flecken, die hinter einem geschliffenen Glas auf dem weißen Tischtuch glitzern. Die Tage eilen, die Ferien sind nahe. Bei Hahns werden keine Reisepläne geschmiedet. Bis eines Tages doch die Reisefreude in das Zimmer tritt und Gastrecht erhält. Else und Hellmut erhalten eine Einladung von Vaters Schwester, sie zu
- 89. besuchen. Die Tante lebt in einem Nest am Thüringer Wald, einem Städtchen, das beinahe in einer Spielzeugschachtel Platz hat, so klein ist es. Und klein ist auch der Tante Häuschen, winzig ihr Geldbeutel, doch groß ihre warme Güte. Sie hat die Sehnsucht in der Schwägerin Brief verstanden und gedacht: zwei bring' ich zur Not unter und durch; wenn es doch alle sein könnten! Die zwei, die kommen dürfen, sind selig. Sie fahren am ersten Ferientag zur Stadt hinaus. Strahlender als mancher, der eine Weltreise macht und denkt, wenn sie nur recht viel Geld kosten möchte, damit ich etwas los werde, sitzen sie in der vierten Klasse. Sechs Stunden Fahrt, vier Wochen Ferien, was sind alle Freuden der Welt dagegen! „Und wir reisen auch“, sagt der Vater, als er mit seiner Frau vom Bahnhof aus heimkehrt. „Nächsten Mittwoch früh bis nach — Schönblick.“ Ach du lieber Himmel, diese weite Reise! Drei Haltestellen weit liegt Schönblick am Rand eines Kiefernwaldes. Sandweg bis hin, karg die Natur, äußerste Bescheidenheit gab ihm den Namen. Doch als Frau Marie, trotz des heiteren Tons, den Kummer in ihres Mannes Augen sieht, ihr nur so eine dürftige Freude bieten zu können, lächelt sie tapfer und sagt ganz heiter: „Ich freu' mich darauf.“ Den Zwang zur Freude haben die kleine Marie und Ferdel nicht nötig. Sie jauchzen laut, denn die Geschwister haben so viel von ihrer Reise erzählt, daß nun auch in ihnen die Lust erwacht ist, zu reisen, und Ferdel schreit wieder: „Will mit der Puffpuffbahn fahren.“ Und flink rutscht er Stühle zusammen, Marie muß einsteigen, ihre Puppenkinder dazu, ein Sofakissen wird freundlich zur Mitfahrt eingeladen, und fort geht die Reise. „Wohin?“ — „Schönblick.“ „Und weiter?“ — „Balin!“
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