Illumination
Engineering
Importance
of Lighting
in Human Life
UNIT 1
Optical System of Human Eye
The eye is an adaptive optical system
comprising of a cornea and a lens.
 The crystalline lens of the eye changes its
shape to focus light from objects OVER A
great RANGE OF distances on the retina.
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Optical System of Human Eye
Cornea
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The transparent front part of the eye
Cornea plays the most important part in
refraction.
It is almost spherical with an outer radius of
curvature of about 8 mm In humans
Cornea contributes most of the eye's focusing
power, its focus is fixed.
The curvature of the lens can be adjusted to
"tune" the focus depending upon the object's
distance.
Optical System of Human Eye
Pupil
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The pupil is the black central circular opening in the iris
it contains groups of smooth muscles that contract and
dilate the pupil.
the pupil acts as an aperture that controls the amount of
light flux that forms images on the retina.
The aperture stop affects several optical processes
the pupil affects the quality of the image through its
influence on aberration, ocular depth-of-focus, and
diffraction.
The pupil has a black appearance and the reason why it is
black is due to the fact that the light the pupil allows to
enter the eye does not exit the eye, instead it is absorbed
by the retina
the pupil diameter is primarily influenced by the ambient
lighting. other factors are old age, drugs, emotions etc
Optical System of Human Eye
Lens
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The lenses of the eye are thicker at the center than at the
edges.
The lens is made up of fine hexagonal fibers that stretch in
the interior of the posterior pole of the lens.
The lens is bi-convex
The eye lens can adjust its shape by the action the ciliary
muscles, which causes eye accommodation, hence
maintaining focus on the retina for objects at varying
distances.
The lens is the only optical component of the eye that
continuously grows with age.
The focal length can be adjusted in order to focus objects
over a wide range of distances through a process knows as
accommodation.
Changing the shape of the eye decreases the radius of
curvature, which in turn changes the focal length
Optical System of Human Eye
Retina
 The retina is the light-sensitive portion of the
optical eye, where images are formed.
 It is connected to the brain through the optic
nerve.
 The retina optimizes the performance of the
eye by wave guiding on-axis and off-axis via
its curvature.
 It is made up of cones and rods, where the
rods are sensitive to vision of low light levels,
but they cannot distinguish colors.
 The cones are sensitive to vision at higher
light levels, and they distinguish colors
Optical System of Human Eye
Image Formation
 After entering into the eye through the cornea, light
is refracted by the cornea and lens.
 Accommodation is the process by which the shape of
the lens can be altered to change its power when the
eye needs to focus at different distances.
 The iris is controlling the amount of light rays enter
into its opening which is called pupil by it’s aperture
stop mechanism.
 This aperture stop is a very important component of
an optical system, affecting a wide range of optical
processes.
 The light beam projected to the Retina
 The image on the retina is inverted like a camera and
is connected to the brain by the optic nerve.
Optical System of Human Eye
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Accommodation is the adjustment of the
optics of the eye to keep an object in
focus on the retina as its distance from
the eye varies
Accommodation of human visual
system
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Visual adaptation is typically defined as a
brief and temporary change in sensitivity
or perception when exposed to a new
stimulus, and by the lingering after effects
when the stimulus is removed
Adaption
Good Effects:-
Good and Bad Effects of Light
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Artificial lights have revolutionized the way
humans live their day-to-day lives.
We’ve moved beyond the sun’s natural cycle
and rely heavily on street lights, light bulb
fixtures and flashlights.
It causes “light pollution”.
In big cities especially, the concept of “night”
is almost obsolete because artificial lights are
kept lit throughout the night.
Human and environmental health is suffering
from this boom of artificial lighting.
Good and Bad Effects of Light
1.The Downside of LEDs
 LEDs are composed of light from all
wavelengths, they resemble sunlight
 These bright lights can disrupt human
circadian rhythms and interfere with
sleeping patterns
 LEDs negatively affect humans and other
species by stimulating the brain to wake
up at night.
Bad Effects of Light
2.Threat to Human Health and Circadian Clock
 The circadian cycle is crucial for human health
because our bodies follow it for other biological
functions such as cell regulation and hormone
production.
 When artificial light continually disrupts our
circadian cycle many severe health problems
could arise.
 People are more prone to cardiovascular disease,
depression, insomnia, and many other sleep
disorders.
 Constant exposure to artificial light can also
make melatonin production irregular, and in
worst case scenarios may cause cancer.
Bad Effects of Light
3.Harmful for Insects and Bats
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Insects are attracted to artificial light and spend
extended periods of time around street lights and
other bulbs.
a large number of insects end up dying because of
the burning heat from the lights.
The gravitation of insects towards street lights also
has negative repercussions on the bat population.
Some bat species are light-averse and are highly
repelled by artificial light sources.
Since more and more insects are gravitating
towards artificial lights, bats have less food to eat.
Bad Effects of Light
4.Confusion for Proper Plant Growth
 Flowering plants and trees need a certain
amount of time in the darkness for proper
development and growth.
 This specific photo period for plants is
important for leaf shape, growth, and overall
development.
 But with excessive light pollution their photo
periods are constantly disturbed.
 This has cascading effects on the pollinating
insects and other species that rely on trees
and flowering plants.
Bad Effects of Light
5.Distraction for Migrating Birds
 Bright city lights can be misleading for
nocturnal migratory birds.
 These migrating birds travel at night and use
the setting sun and moon to navigate their
route.
 Light pollution can confuse birds into thinking
the lights are navigators and they can end up
colliding into a building.
 Many migrating birds die from these collisions
or become injured enough to be left for other
predators.
Bad Effects of Light
6.Disruption for Freshwater and Marine Life
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In rivers that run near or through cities, the
migratory patterns of fish are increasingly disrupted.
Light pollution confuses fish and has affected their
foraging, predation, shoaling and reproductive rate.
Marine ecology has also become negatively affected
by artificial lights.
When female sea turtles move to beaches to lay their
eggs, they are put-off by any nearby lights.
They want to lay their eggs in areas that are darker
and less exposed, but sometimes artificial lights can
be an obstacle.
The bright lights negatively affect female sea turtles
and their young.
Bad Effects of Light
7.Disturbance for Amphibian Reproduction
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Frogs are nocturnal amphibians that also go
through periods of hibernation.
This hibernation period is also when they
reproduce.
Artificial light has begun to disrupt their
reproductive cycles.
It alters their senses to know when to breed and
when to return to their home.
As they become more desensitized, the frogs are
missing their windows of opportunity to
reproduce.
So they face breeding declines.
Bad Effects of Light
8.Difficulties for Astronomers
 Artificial lights pose problems for scientists
and researchers who want to observe and
document objects in the night sky.
 Light pollution makes the sky brighter and
makes it harder for them to take a smooth
spectra.
 Their ability to study the night sky has
been hindered by the overwhelming
number of bright city lights.
Bad Effects of Light
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Exposure to natural light helps our bodies
produce Vitamin D
Improves our circadian rhythms and sleep
patterns
Helps us to focus
Enables us to get more done and even
makes us happier.
Ensuring we get enough of this vital
resource is key to our physical and
psychological wellbeing
Good Effects of Natural Lighting
Natural light gives us Vitamin D
Natural light improves our productivity and
focus
 Natural light helps our body clock keep time
 Natural light improves psychological wellbeing
 Natural light can benefit our buildings
(wellness architecture)
 Natural light can improve energy efficiency
 Natural light can help prevent mildew
 Natural light could be central to future
designs
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Good Effects of Natural Lighting
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Light Perception
Colour Perception
Directional Perception
Perception of shapes
Perception of space
Perception of movement
Perception of reflectivity
Characteristics of Human Visual
System
Visual Acuity
Ability to distinguish fine details
 Contrast
Relation between the luminance of an
object and its immediate background.
L1 – L2
ΔL
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or
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L1
L1
L1 is luminance of background
L2 is luminance of the object
Acuity and Contrast
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High Hazard
Artificial optical radiations
Harmful even for momentary exposure
Can cause erythema, photo keratitis, photo retinitis,
cataract
Medium Hazard
Artificial optical radiations
Very bright light sources or thermal discomfort
Lamps which emit infra red radiation
It do not pose a retinal hazard within 10 sec
Low Hazard
Optical radiations which do not pose a hazard on normal
exposure
It do not pose a retinal hazard within 100 sec
Optical Radiation Hazards
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Professional Projection Systems
Intense Pulsed Light (Cosmetic use)
Search Lights
UV curing of paints,printing ink
Welding
UV from Plasma cutting
UV Lasers
Laser surgery
IR Lasers
IR from welding
Class 3B and 4 lasers
High Hazard
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Task lighting from fluorescent strips
without diffusers
Desk-top projectors
High Pressure Mercury Vapour Lamp
Flood lights, spot lights
Vehicle headlights
UV inset traps
1M,2M,3R Lasers
IR fromfurnaces
Medium Hazard
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Task lighting from fluorescent strips with
diffusers
Local task lights
LED Remote control devices
Vehicle side, brake and indicator lights
Photocopiers
Computer display screens
Class 1 Lasers
IR from artificial heater
Low Hazard
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Use filters,screens,curtains,remote
controls etc
Train the workers and give instructions
Organise work to reduce exposure
Restrict access to hazardous areas
Use protective equipments like goggles,
face shields
Use relevant safety signs
To minimize Optical Hazard
radiations
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To visualize different objects
Traveling during night hours
To carry out various tasks at home, office,
workshop, industries,hospital etc
In quarries, mines, tunnels, etc
Traffic controls on roads, railway signaling
In Schools, theatres, auditoriums etc
Consumption of light decides the standard
of living in that country
Dependence of human activities
on Light
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Sun Light
Sky Light
Moon Light
Lightening
Artificial Lights
Generation of Light
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Incandescence
Electric Discharge
Phosphorescence
Fluorescence
Chemiluminescence
Bioluminescence
Triboluminescence
Production of Light
Metal is continued to be heated
 Glows from red-orange-yellow-white-blue
 These colors present a source of light
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Incandescence
Neon Lights produce light due to gas
discharge
 When electric current passes through
certain gases, a colored glow is produced
 Neon-red
 Argon - violet
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Electric Discharge
Materials coated with phosphorous
absorbs ultra violet rays
 When there are no UV rays(in dark),
these materials produce light
 Such materials have a capacity to hold on
the light for certain period of time
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Phosphorescence
Fluorescent lamps release their absorbed
UV light, right away
 The products which claim to whiten or
brighten uses fluorescence
 Eg:- highlighters, laundry detergents
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Fluorescence
Known as cold light
 By product of a chemical reaction
 Produces no heat, only light
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Chemiluminescence
Chemiluminescence occurring in living
organisms
 Fire flies, some types of fishes
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Bioluminescence
Produces when certain crystals are rubbed
together or crushed or scratched
 Momentary light
 As soon as the process of rubbing stops,
no more lights are produced
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Triboluminescence
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How artificial light is substitute to natural
light??
How artificial light is substitute to
natural light?
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Illumination level is not sufficient
Not available during evening, night hours
Natural light is not consistent
In cloudy atmosphere
In tunnels
In quarries,mines
To avoid glare in summer
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Availability-Day/night
Cloudy atmosphere
Controlling the light
Steady output
Availability-Quarries/Mines
Glare
Designed for specific task
Compare Artificial Light with
Natural Light
Natural lighting, also known as
daylighting, is a technique that efficiently
brings natural light into your home using
exterior glazing (windows, skylights, etc.)
 It reduces artificial lighting requirements
and saves energy.
 Natural lighting has been proven to
increase health and comfort levels for
building occupants.
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Methods to control natural light
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Use fibre roofs, fibre sheds in passages,
stairs, kitchen etc
Use frosted glasses for windows in offices
and homes
Sun breaks
Sun goggles
Zig zag designs for roofs
Methods to control natural light
SUNLIGHT SHADING METHODS IN
BUILDINGS
1. Extended porch
2. Glazed glasses on top of house ceiling
(used in stair cases)
3. Bahama shutter
4. Roll blinds of fibre can be fixed on window
frame
5. Fix Window where tree covers the sunlight
6. Side blockers can be used in windows
which blocks direct sunlight
Methods to control natural light
Extended Porch
Glazed windows reduce the loss of heat
during winter and coolness during
summer
 they allow air conditioners and central
heating units to work less and still
maintain the building at a constant
temperature
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Glazed glasses on top of house
ceiling
superior protection from high winds and
heavy rain also
 they are mounted outside of the house,so
they shut out storms effectively
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Bahama shutter
Tilted roll blinds of fibre fixed on
window frame
Sun Control with Trees
Side Blockers
Sr No
Location
Illumination Required
1
Lobbies
2-5 lux
2
Store rooms
5-10 lux
3
Reception/Waiting Rooms
10-20 lux
4
Industrial works
50-100 lux
5
Different tasks
100-200 lux
6
Medical/surgical
1000-2000 lux
Perfect Level of Illumination
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Travel in straight lines
Reflection
Refraction
Absorption
Transmission
Polarisation
Properties of light
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Explain the properties of light to the class
Activity:
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Wavelength
Colour
Flux density(illuminance)
Degree of polymerisation
Colour temperature
Luminous intensity
Luminance
Reflectance
Transmittance
Unit and Equipments to measure
different terms related to light
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Prepare the table with unit and instrument
used to measure different terms related
to light.
Activity:
Most photometers detect the light
with photoresistors, photodiodes or photo
multipliers.
 To analyze the light, the photometer may
measure the light after it has passed
through a filter or through
a monochromater for determination at
defined wavelengths or for analysis of
the spectral distribution of the light
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A photoresistor (also known as
a photocell, or light-dependent
resistor, LDR, or photo-conductive cell) is
a passive component that decreases
resistance with respect to receiving
luminosity (light) on the component's
sensitive surface
Photo resistors
A photodiode is a light-sensitive
semiconductor diode.
 It produces current when it absorbs
photons.
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photodiode
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A photomultiplier is a device that
converts incident photons into
an electrical signal.
photomultipliers
For the quantification of light we use
Photometers
 Or to measure the candle power of light
we use photometers
 The candle power of a light source is
compared with a known standard candle
power source
 Based on inverse
Square Law
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Photometers
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Photometer head is moved in between the
sources
Movement of photometer head by trial and
error method is continued and stopped at a
place where illumination at both sides of the
screen is same
Candle powerof the source=S * (l2^2/l 1 ^2)
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S-candle power of std source
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L1 – distance of std source from photometer
head
 L2- distance of light source from photometer
head
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Polar Photometer
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Photocell
Arm
Rotating mechanism
Rotatable platform
Vertical Adjustment
Luminate
Mirror
Components
Photocell is mounted on the end of an
arm which is capable of being rotated
about the luminaire to give
measurements of luminous intensity at
known angles
 The luminaire is firmly attached to a
rotatable platform, enabling readings at
any angle
 The light to be measured should reach the
photocell
 Baffles are used on the front of photo cell
housing to restrict the field of view
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The optical path length should be 5 times
the largest dimension of the luminaire
being tested
 By using a mirror it is possible to lengthen
the optical path, if there is restriction for
size of photometer
 Measurement of luminous intensity is
made by taking readings of the
photocurrent at the required angle
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Flood lights , projectors and other
concentrating beams have to be tested
with greater distance than indoor
luminaries
Gonio Photometer
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Explain Goniophotometer
Activity
A Goniophotometer is a device used for
measurement of the light emitted from an
object at different angles.
 The use of goniophotometers has been
increasing in recent years with the
introduction of LED-light sources, which
are mostly directed light sources, where
the spatial distribution of light is not
homogeneous.
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Goniophotometer
 Applications:
a. Measurement
of luminous flux of a light
source
b. Measurement of luminous
intensity distribution from a source much
smaller than the size of the
goniophotometer
 Using color sensors additional characteristics
can be measured
a. Distribution of correlated color temperature
b. Color uniformity
Goniophotometer
QUESTIONS
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Q1. Explain the optical system of human eye with a
neat sketch.
Q2. Explain the generation of light?
Q3. What are good and bad effects of lighting
Q4. Classify the optical radiation hazards.
Q5. Explain the dependence of human activities on
light.
Q6. Explain accommodation and adaption in
connection with visual mechanism and optical system
Q7.What are the different properties of light?
Q8.Compare Natural light with artificial light.
Q9.Define the four procedures of photometry?
Q10.How can we quantify light?
Important Questions
IN SEM PAPER
End Sem Paper
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