2-7 Introduction to lighting techniques 2024S.pdf

AV Production Technologies
2.7 Introduction to lighting
Spring 2024
Mireya Fernández
Departament TSC / Departament EE
TelecomBCN — UPC

Table of contents
Introduction light and lighting
1. Physical aspects
2. Psycho-Sensorial aspects
3. Basic characteristics of light

Light: electromagnetic wave
• Is the only part of electromagnetic spectrum that we can see
• color is a perceptual quality of light
• The human eye can distinguish about 10 million colors!!
Physical aspects

Physical aspects
Interaction of light and matter
• Photons may give their energy to the material (absorption).
• Photons give their energy, but photons of identical energy are
immediately emitted by the material (reflection);
• The wave is scattered by the material (dispersion)
• Photons may not interact with the material structure (transmission)
• During transmission there are changes in velocity (refraction).
Interaction of photons with the electronic or crystal structure of a material leads
to a number of phenomena:
At any instance of light interaction with a material, the total intensity of the
incident light striking a surface is equal to sum of the absorbed, reflected,
and transmitted intensities i.e.
𝐼𝑜 𝐼 𝐼 𝐼

Interaction of light and matter
Materials are classified on the basis of their interaction with visible light into
three categories.
Materials that are capable of transmitting light with
relatively little absorption and reflection are called
transparent materials i.e. we can see through them.
Translucent materials are those through which light
is transmitted diffusely i.e. objects are not clearly
distinguishable when viewed through.
Those materials that cannot transmit the visible light
are termed as opaque materials. These
materials absorb all the energy from the light photons
Physical aspects

Refraction
When the light photons are transmitted through a material, they causes polarization of
the electrons and in-turn, the speed of light is reduced and the beam of light changes
its direction. Due to change of medium, the phase velocity of the wave is changed but its
frequency remains constant. This is most commonly observed when a wave passes from
one medium to another at any angle other than 90° or 0°
The relative velocity of light passing through a medium is expressed by the optical
property called the index of refraction (n), and is defined as:
𝑛
where c0 is the speed of light in vacuum and c the speed of light in the concerned material.
If the angle of incidence from a normal to the surface is α, and the angle of refraction is β,
the refractive index of the medium, n, is given by (provided that the incident light is coming
from a phase of low refractive index such as vacuum or air) :
𝑛
sin 𝛼
sin 𝛽
α
β
n
The speed of light in a material can be related to its electrical
and magnetic properties as: 𝑐
.
Thus, 𝑛
.
𝜇 𝜀 Since most materials are only
slightly magnetic (μr ≈1) thus 𝑛 𝜀
Physical aspects

Refraction
n1 , n2 index of refraction , α angle of incidence, β angle of refraction
α α
𝑛
𝑛
β
Refracted Ray
Snell’s law of light refraction: refractive indices for light
passing through from one medium with refractive index
n1 through another of refractive index n2 is related to the
incident angle, α, and refractive angle, β, by :
𝑛
𝑛
𝑠𝑖𝑛𝛽
𝑠𝑖𝑛𝛼
The refraction changes in function of the wavelength. Short wavelengths (like blue and violet) are
transmitted more than long ones (like red). This phenomenon is used to split the white light in its
components (when goes through a refraction prism), originating the dispersion of light.
Physical aspects

Reflection
Reflection is the change in direction of a wave-front at an interface between two
different media so that the wave-front returns into the medium from which it
originated. When the light is reflected some percentage of energy is lost due to the
absorption phenomena. The ratio between the reflected and incident light is called
reflectance or reflectivity. Any not totally black surface can reflect the light.
𝑅
𝐼
𝐼
𝜃 𝜃
𝐼 𝐼 𝑅𝐼
𝑛
𝑛
𝑅
𝑛 𝑛
𝑛 𝑛
The above equations apply to the reflection from
a single surface and assume normal incidence.
The value of R depends upon the angle of
incidence.
• Materials with a high index of refraction have a higher reflectivity than materials with
a low index. Because the index of refraction varies with the wavelength of the
photons, so does the reflectivity.
• In metals, the reflectivity is typically on the order of 0.90-0.95, whereas for glasses it
is close to 0.05.
• High reflectivity is desired in many applications including mirrors, coatings on
glasses, etc.
Physical aspects

Reflection
Regarding the nature of reflected rays there are 4 different kinds of reflection: specular,
diffuse (light scattering), compound, and mixed.
SPECULAR COMPOUND DIFFUSE MIXED
SELECTIVE
Regarding the reflected wavelengths:
Selective or chromatic when the
reflection is not the same for all the
wavelengths.
Non-selective or achromatic when
all the wavelengths are reflected
equally.
Black surfaces R=0
Medium Gray surfaces R =0.5
White surfaces R=1
NON-SELECTIVE
Physical aspects

Absorption is the transformation of electromagnetic energy in other form of energy
typically heat. Is a characteristic of all non totally reflective surfaces, and of non
transparent materials.
Absorption
When a light beam impacts on a material
surface, a portion of the incident beam that is
not reflected by the material is either absorbed
or transmitted through the material.
Bouguer’s law: The fraction of beam that is absorbed is
related to the thickness of the materials and the manner in
which the photons interact with the material’s structure:
where
I = intensity of the beam coming out of the material
I0 = intensity of the incident beam
x = path through which the photons move
α = linear absorption coefficient, which is characteristic of a
particular material.
α α
𝑛
𝑛
β
Refracted Ray
I0
R.I0
(1-R).I0
(1-R).I0 .e-αx
Absorption
𝐼 𝐼 𝑒
Physical aspects

The absorptance (not absorbance) of a material is the effectiveness in absorbing radiant
energy. It is defined as the ratio of the light absorbed by a body to that incident upon it.
𝐴 𝑙𝑜𝑔
𝐼 λ
𝐼 λ 𝑒
log 𝑒 𝛼𝑥𝑙𝑜𝑔 𝑒 0.4343𝛼𝑥
The color of objects is due to the selective absorption (absorption of some wavelengths),
that explain for example why the ocean is blue.
Absorption
When sunlight hits the ocean, the water
strongly absorbs long-wavelength colors at the
red end of the light spectrum, as well as short-
wavelength light, including violet and ultraviolet.
Blue light is strongly scattered.
Physical aspects

Absorption filters are made primarily from
colored filter glass or synthetic gels, and
represent the largest class and most widely
used type of filters for applications that do not
require a precise definition of transmitted
wavelengths. Commonly utilized to isolate a
broad band of wavelengths, absorption filters
are also helpful to block short wavelengths
while transmitting longer ones.
Color Compensating, Conversion, and
Balancing Filters
Belonging to the category of absorption filters,
color compensating, conversion, and light
balancing filters are most often utilized to
modify the color temperature of tungsten and
tungsten-halogen illumination. They are used
to create special effects in a number of
photography applications and are widely
employed in the cinema industry.
Absorption
Physical aspects

Transmission
Transmission Is the pass of the light through a media without frequency change in
the monochromatic radiations that compose the light. This phenomenon is
characteristic of some glasses, crystals, plastics, the water and other liquids and the air
among other media. The fraction of light beam that is not reflected or absorbed is
transmitted through the material. The process of light transmission is as follows:
α α
𝑛
𝑛
β
Refracted Ray
I0
R.I0
(1-R).I0
(1-R).I0 .e-αx
R.(1-R).I0 .e-αx
Absorption
I0.(1-R)2. e-αx
The ratio between the incident and the
transmitted light is the transmittance of the
media:
𝑇
𝐼 1 𝑅 𝑒
𝐼
It is measured at a specific wavelength
Physical aspects

Transmission
There are three different kind of transmission: regular, diffuse and mixed.
Regular transmission occurs in transparent media those that allows light to pass through
them without any change. Objects can be seen through transparent media.
In diffuse transmission the incident light is diffused in the media, and exits of it in several
directions. This transmission occurs in translucent materials those that only allows light
to pass through diffusely.
REGULAR DIFFUSE MIXED
Physical aspects

Dispersion
Dispersion is the phenomenon in which the phase velocity of a wave depends on its
frequency, or alternatively when the group velocity depends on the frequency. Media
having such a property are termed dispersive media. Dispersion is sometimes called
chromatic dispersion to emphasize its wavelength-dependent nature.
Prisms use glass with a high index of refraction to exploit the variation of refraction with
wavelength. Blue light refracts more than red, providing a spectrum that can be isolated
using a narrow slit.
Physical aspects

The art of cinematography is the art of lighting
and making that light tell the story.
Stephen H. Burum, ASC
(Apocalypse Now, Mission Impossible, etc.)
Lighting: can emphasize important details or hide them It can flatter a subject by bringing
out positive attributes and it can de-emphasize or hide less attractive attributes. Lighting
can even impart a sinister and hostile look. It can invent spaces, alter distances and
create a determinate atmosphere among other effects.
• quantity of light
• quality of light
• direction of light
• color
https://www.youtube.com/watch?v=c4170ZIdG_I&t=24s
The lighting process for production is based in
4 parameters:
Psycho-Sensorial aspects

• In optics, radiometry is a set of techniques for measuring electromagnetic radiation,
including visible light. Radiometric techniques characterize the distribution of the
radiation's power in space.
• Photometry is the science of the measurement of light, in terms of its perceived
brightness to the human eye. It is concerned with humans’ visual response to light
• Radiometry is concerned with the total energy content of the radiation, while photometry
examines only the radiation that humans can see.
• Thus, the most common unit in radiometry is the watt (W), which measures radiant flux
(power), while the most common unit in photometry is the lumen (lm), which measures
luminous flux. For monochromatic light of 555 nm, 1 watt = 683 lumens. For light at
other wavelengths, the conversion between watts and lumens is slightly different,
because the human eye responds differently to different wavelengths.
Radiometry & Photometry
Basic characteristics of light. Quantity of light

The following table summarizes the most common radiometric and photometric quantities,
along with their symbols and units.

The path that follows the light from the source, to the camera (or the eye) is
composed by 4 stages:
• the light source emits light (luminous flux)
• with a determinate intensity
• the light reaches a surface and illuminates it with a certain illuminance
•The light is reflected by the surface with a certain luminance
[Radiant flux]
Watt/sr
[Irradiance]
Watt/cm2
[Radiance]
Watt/cm2/sr
[Radiant intensity ]
Watt/sr

In photography, cinema and television, the word contrast is applied to at least 4 different
concepts: scene or luminance contrast, camera contrast, lightning contrast and image
contrast.
a) The luminance contrast is the relationship between maximum and minimum
luminance levels in the scene, that is clearest and darkest elements in the scene.
b) Camera contrast: is the maximum difference in luminance that the recording system
can afford.
c) Lighting contrast: once the point of view is set, (that is the camera is placed), the
lighting contrast is the relationship between the light coming form two different
sources illuminating the same subject. (for example is key light is twice than fill light
the contrast is 2:1)
d) Image contrast: is the relationship between maximum and minimum luminance levels
in the reproduction system (display) that many times is adjustable by the user to set it
to its preferences.
Contrast

The variations in the quality and moods of lighting are nearly infinite, think on many
adjectives we can apply to it:
• indirect/direct
• hard/soft
• specular /diffuse
• ambient /sourcey
• flat / chiaroscuro
• shadowy /high key
• focused /general
• modulated /plain
• strong /gentle
• contouring /frontal
• punchy /wrapping …
Not all are precisely defines, but all contribute to create a determinate sense of mood ore
atmosphere in the scene. The major variables that are involved in a creative lighting
process are the hard/soft light.
Basic characteristics of light. Quality of light

The most important factor in the relative hardness/softness of a light is the size of the
radiating source relative to the illuminated object. The smallest source, the hardest light
is, and it would create shadows, while the larger is the light source it tends more to wrap
the object and to produce a soft light effect. Hard Light is obtained when the light is
transmitted directly from a small point source resulting in relatively coherent (parallel)
rays. Soft Light (or diffused) light has the opposite effect. Diffusers are used over the
front of lights to soften and diffuse their beams. At the same time, diffusers also reduce
the intensity of light.
Hard light Soft light (the same light source with a diffusor)
Hard/soft light

Hard light
increase the contrast of the
object. increase the saturation
of the
Hard/soft light
Soft light
still increases the contrast of
the object a little.
Diffused light
the light does not show any
direction anymore. There
are not shadows.

The height of the light source relative to the subject is an important point.
As a broad generalization, lights that are higher , are going to create more shadows and
hence more shape. As within direction, the farther away from the axis of the lens,
(camera) the more likely to create shape, depth and texture.
Altitude relative to the subject
(d) high side (e) high (f) top light.
(a) light on the ground (b) very low (c) side

The direction from which light hits the subject is crucial to the quality of light. It is perhaps
the key determinant of how the light interacts with the shape and texture of the subject.
Direction relative to the subject
(a) back light (b) 3/4 back (c) side
(d) 3/4 front (e) front light

Pros:
Provides the most information to
the camera by lighting the entire
scene.
Cons:
lack volume and depth. Textures
and details are minimized.
Scenes appear flat with few
shadows.
Pros:
Perfect to emphasize texture, dimension,
shapes, or patterns.
Can separate the subject from the background.
Cons:
May be too severe for some subjects, creating
some areas that are too bright, and some that are
too dark.
Side 3/4 front front light

Pros:
Simplifies a complicated scene by emphasizing the subject.
Provides a flattering halo of light in subjects. Adds strong shadows in scenes.
Cons:
Lack of detail in a dark subject.
back light 3/4 back

Color
The perception of color is a complex phenomenon that involves physics of light the nature
of physical matter, the physiology of the eye and its interaction with the brain. There are
two types of photoreceptor cells in the eyes: cones and rods.
In very low light levels, vision is scotopic: light is detected by rod cells of the retina. In
brighter light, such as daylight, vision is photopic: light is detected by cone cells which are
responsible for color vision. Cones are sensitive to a range of wavelengths, but are most
sensitive to wavelengths near 555 nm. Between these regions, mesopic vision comes into
play and both rods and cones provide signals to the retinal ganglion cells. The shift in color
perception from dim light to daylight gives rise to differences known as the Purkinje effect.
The retina contains three types of color receptor
cells, or cones. S cones, are most responsive to
light that is perceived as blue or blue-violet
(wavelengths around 450 nm); M cones are most
sensitive to light perceived as green (wavelengths
around 540 nm); L cones, are most sensitive to
light that is perceived as greenish yellow,
(wavelengths around 570 nm). Rods are
maximally sensitive to wavelengths near 500 nm
(R curve), and play little, if any, role in color vision
are responsive to wavelengths of

Color
The Purkinje Effect is the tendency for the peak luminance sensitivity of the eye to
shift toward the blue end of the color spectrum at low illumination levels as part of dark
adaptation. In consequence, reds will appear darker relative to other colors as light
levels decrease. This effect introduces a difference in color contrast under different
levels of illumination. For instance, in bright sunlight, geranium flowers appear bright
red against the dull green of their leaves, or adjacent blue flowers, but in the same
scene viewed at dusk, the contrast is reversed, with the red petals appearing a dark red
or black, and the leaves and blue petals appearing relatively bright.
Photopic vision Mesopic vision Scotopic vision
night scenes have a bluish hue

Color
The visible spectrum perceived from 390 to 710 nm

The color of the objects is a combination of the color of the light and the nature of the
material it is falling on and being reflected by. (essentially the color of an object is the
wavelength that it do not absorb. )
Additive and subtractive color.
Sunlight appears white (it contain all the colors).
Light is an additive system color. Red Green
and Blue are the primary colors, and when mixed
in pairs produce Magenta, Yellow and Cyan. The
additive color system involves light emitted directly
from a source before an object reflects the light.
Paint is a subtractive color system the primaries
are Magenta Yellow and Cyan. The mixing of all
color removes the light and produces a muddy
gray brown theoretically black
additive color subtractive color
Color

Qualities of color
Color has four basic qualities: hue, value, saturation and temperature. The first three
are physical properties and are often called the dimensions of the color. The last is a
psychological aspect of color, and is the most common system used in film and video to
describe the color of a light.
Color
•Hue: is the essential quality that
distinguish one color from another and that
corresponds to the predominant
wavelength. The average person can
distinguish around 150 distinct hues. In
video is called “phase” and is measured
around a circle from 0º to 360º.
•Value: is the relative lightness or darkness
of a color. The average person can
distinguish 200 value changes.
High value
Low value

Qualities of color
Color
•Saturation: is the strength of the color or
relative purity of a color (its brilliance or
grayness). Any hue is brightest in its pure
state, when no black or white has been
added. The average person can see only
about 20 levels of saturation change.
•Color temperature: The temperature is
the relative warmth or coldness of a hue.
This derives from the psychological
reaction to the color( red or red/orange are
the warmest and blue or blue/green are the
coolest.

What is white?
The eye will accept a wide range of light as white, depending on external factors
(environmental) and adaptation (psychological) . The color meter will tell us that there are
enormous differences in the color of light in a room lit with tungsten light, or lit with
ordinary fluorescents. Our perception tell us that there is white light, and without a side by
side comparison the eye is not a good indicator of what is a white light. Unfortunately,
film emulsions and CCD’s are very sensitive to this fact, and an absolute color reference
is essential.
Control of color

What is white?
The quality of the reproduction of colors is termed color rendition, and measured by
the color rendition index (or color rendering index). Continuous spectra have a very
good color rendition. Linear spectra only permit one single color to be perceived well.
Multiline spectra reproduce several colors of the relevant spectrum well, but in the
intermediate areas the color rendition is weaker.
Blue and green colors appear comparatively grey and matt under warm white
incandescent light despite excellent color rendition. However, these hues appear clear
and bright under daylight white light from fluorescent lamps – despite poorer
color rendition. When rendering yellow and red hues, this phenomenon of respective
weakening and intensifying of the chromatic effect is reversed.
Control of color

The reflectance curve of a sweater (green curve) and the wavelengths
reflected from the sweater when it is illuminated by daylight (white) and by
tungsten light (orange).
Control of color

Incandescent lamp
Continuous spectra: good
color rendition.
CRI = 100
Control of color
Daylight
Continuous spectra: good
color rendition.
CRI =100
Fluorescent lamp
Discharge lamps have
line spectra : “bad” color
rendition
CRI <100.

Color Temperature
In film and video production, the most common system used in describing the color of
light is the color temperature.
This scale is derived from the color of a theoretical black body or Planckian radiator
An incandescent light bulb approximates an ideal black-body radiator, so its color
temperature is essentially the temperature of the filament.
For colors based on black body theory, blue occurs at higher temperatures, while red
occurs at lower, cooler, temperatures. This is the opposite of the cultural associations
attributed to colors, in which "red" is "hot", and "blue" is "cold
Control of color

Typically the light color is measured on a scale known as color temperature
(blue-orange axis), as well as along a green–magenta axis orthogonal to
the color temperature axis. Color meters measure this two axes separately.
Most colored light is a combination of various
wavelength; there is no one number that can
describe the color accurately. Most color meters
give two readouts, one from the red/blue scale
and one from the magenta/green scale (they are
called three color meters because they measure
red, blue and green).
Control of color

Meters give the color temperature in Kelvin.
Many times, the readout in the magenta/green
scale is relative, that is the meter indicates the
amount of filtration needed to correct the color to
normal in the magenta/green scale. This is the
CC index or Color Correction index. Also, they
give the LB index, used to select the right amber
or blue LB filter needed to balance a light source
and compensate its color temperature
KCM3100 color meter from KENKO
Magenta filter
Light balance in mired *
* mired = 106 / color temperature (Kelvin)
Control of color

Color filter blocks passage of some portion of the visible output from any light source or
light reflector by absorbing and transmitting selectively.
The filters that act in the blue-orange axis are called CTB (color Temperature Blue) and
CTO (Color Temperature Orange) filters.
The filters that act in the magenta-green axis are called Minusgreen and Plusgreen
filters. And they are used to correct light coming from fluorescent lamps and other
discharge lamps..
CTO CTB Minusgreen Plusgreen
Control of color

CTB filters are designed to increase the color temperature (measured in degrees Kelvin)
of a light source. Full CTB will typically convert a 3200 K light source to 5500 K, or normal
daylight. There are several graduated steps of CTB filters to achieve the proper color
balance. Typically they are hey are 1/8, 1/6, 1/4, 1/2, 3/4, full and extra.
Control of color

CTO Filters lower the color temperature of daylight or a daylight source to match an
incandescent light source. CTO's are often used on windows to convert daylight to
incandescent light. A 3/4 CTO will typically convert sunlight at 5400 K to 3200 K typical
tungsten. Because sunlight varies in color temperature by region and during the day
from sunrise to sunset, there are several graduated steps of CTO from 1/8 to extra.
Control of color

Minus green filters are designed to reduce the green spike found in fluorescent and
HMI light sources. Minus green filters can be combined with the CTO or CTB filters to
simulate the desired color temperature. Usually they are graded in six steps (1/8, 1/4,
1/2, 3/4, full and extra).
Control of color

Plus Green filters are designed to be added to sources being used as fill lights where
there is a predominance of fluorescent lights that cannot be eliminated. Plus green filters
will reduce the red and blue output of the light source, thus creating a green spike
simulating the fluorescent lamp.
Control of color

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