Light lecture ppt
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This document discusses the factors that are essential for efficient vision and lighting, including sufficient illumination levels, uniform distribution of light, and an absence of glare and sharp shadows. It also covers the principles of natural and artificial lighting, including the different lighting systems, types of lamps, and illumination levels needed for various visual tasks. Key factors mentioned are orientation of buildings for natural light, interior room colors, and the need for lighting to approximate daylight color and be steady without flickering.
Light lecture ppt
- 2. • Light is electromagnetic radiation that can be detected by the human eye. Electromagnetic radiation occurs over an extremely wide range of wavelengths, from gamma rays with wavelengths less than about 1 × 10−11 metres to radio waves measured in metres.
- 6. For efficient vision, the following light factors are essential : (1) SUFFICIENCY -An illumination of 15 to20 foot candles (1 foot candle = 10. 76 Lux) is accepted as a basic minimum for satisfactory vision. (2) DISTRIBUTION-The distribution of light should be uniform, having the same intensity, over the whole field of work. (3) ABSENCE OF GLARE-Glare may be a direct glare from a light source or reflected glare from sources such as table tops and polished furniture. Glare causes annoyance. (4) ABSENCE OF SHARP SHADOWS-Like glare, shadows cause confusion to the eye and therefore should not be present in the field of vision.
- 7. • (5) STEADINESS-The source of light should be constant. It should not flicker because flickering causes eye strain and may lead to accidents. • (6) COLOUR OF LIGHT-The colour of light is not very important so long as the intensity is adequate. Since natural light has a soothing effect on the eye, the artificial light should as far as possible approximate the daylight colour. • (7) SURROUNDINGS-For efficient vision, colour schemes in rooms are important. Ceilings and roofs should have a reflection factor of 80 per cent; walls 50 to 60 per cent; furniture 30 to 40 per cent. There should not be much reflection from the floor, not more than 15 · to 20 per cent. Contrasting colours are often used to prevent accidents, e.g., culverts, bridges, etc.
- 9. • Natural lightinig is derived partly from the visible sky and partly from reflection. • In fact, much light comes to the rooms by reflection from light coloured objects. • Efficient utilization of natural light calls for careful design, location and orientation of buildings and relationship between buildings (town planning). Natural lighting also depends upon the time of the day, season,weather and atmospheric pollution. • Since natural light is accompanied by radiant heat, all attempts should be made to exclude radiant heat while admitting daylight.
- 10. • The following general principles are taken into consideration in planning for the best utilization of daylight- • (1) ORIENTATION-Buildings should be oriented, wherever possible,towards north or south for uniform illumination. This is particularly important in respect of schools, factories and laboratories where uniform lighting is required in all the rooms. When a building faces east and west, window shades are provided to protect against the direct penetration of sunlight. (2) REMOVAL OF OBSTRUCTIONS. (3) WINDOWS-In modern practice, window area is correlated to the purpose the room is intended to serve. A tall window gives greater penetration of light; a broad window gives greater diffusion of light.
- 11. • (4) INTERIOR OF THE ROOMS -In order to obtain the full benefit of the natural illumination, the ceiling should be white; the upper portions of the walls light-tinted; and lower portions somewhat darker so as to give comfortable contrast to the eyes.
- 14. • Artificial lighting should be as close as possible to daylight in composition. • There are five systems of artificial lighting : • -direct, • -semi-direct, • -indirect, • -semi-indirect and • -direct-indirect
- 15. • (1) DIRECT LIGHTING -In direct lighting, 99 to 100 per cent of the light is projected directly towards the working area. Direct lighting is efficient,economical, but tends to cast sharp shadows. It should not fall into the eyes. • (2) SEMI-DIRECT-Here 10 to 40 per cent of the light is projected upwards so that it is reflected back on the object by the ceiling. • (3) INDIRECT-light does not strike a surface directly, because 90 to 100 per cent of the light is projected towards the ceiling and walls. • (4) SEMI-INDIRECT : Here, 60 to 90 per cent of the light is directed upwards, and the rest downwards. • (5) DIRECT-INDIRECT : Here, light is distributed equally.
- 16. • (1) FILAMENT LAMPS-These are widely used. The electric current heats up the tungsten filament and the light emitted depends upon the temperature. The. hotter filaments produce the bluer light. • 5% light// 95% Heat. • (2) FLUORESCENT LAMPS-The lamps consist of a glass tube filled with mercury vapour and an electrode fitted at each end. The inside of the tube is coated with fluorescent chemicals, which absorb practically all the ultraviolet radiation and remit the radiation in the visible range. • 21%light//79% Heat.
- 17. • The eye responds to a range of illumination ranging from • 0.1 lux (full moonlight night) to 100,000 lux (bright sunshine). • A useful rule of thumb is that the illumination level should be 30 times higher than the level at which the task can just be done.
- 18. Visual Task Illumination (lux) Casual Reading 100 General Office Work 400 Fine Assembly 900 Very severe tasks 1300-2000 Watch Making 2000-3000
- 19. 1)Hyperbilirubinaemia of premature infants - as a therapeutic measure. 2) Biologic rhythms of body temperature 3) Physical activity 4) The stimulation of melanin synthesis 5)The activation of precursors of vitamin D 6) Adrenocortical secretion and 7)food consumption
- 20. • 1) Poor light causes eye strain,headache,lacrimation,interferes with efficiency,eye-fatigue. • 2)Glare can also cause eye strain,accidents,reduce critical vision. • 3)Infrared Rays can cause burn and eye cataract ,chronic inflammation of the lids (common in glass workers ) • 4) Ultraviolet Rays can cause infalammation of the cornea & conjunctiva,pain & running eye (common in welders ).