LECTURE 01 Illumination
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Transcript of LECTURE 01 Illumination
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ILLUMINATION
Engr. Mrs. Munira Batool
MS Electrical Engineering
Lecturer EED, UET Taxila
1Power Distribution and Utilization
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This lecture covers
Illumination basics
Laws of Illumination
Power Distribution and Utilization 2
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Historical Background
With the discovery of fire, the earliest form of artificiallighting used to illuminate an area were campfires or torches.
Prehistoric people used primitive lamps to illuminate
surroundings. These lamps were made from naturally
occurring materials such as rocks, shells, horns and stones,were filled with grease, and had a fiber wick. Lamps typically
used animal or vegetable fats as fuel.
Oily animals (birds and fish) were also used as lamps
Candles and glass lamps were also invented. With the development of electricity and the incandescent
light bulb, the luminosity of artificial lighting improved
enough to be used indoors.
Power Distribution and Utilization 3
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Definition
Lighting or illumination is the deliberate use
of light to achieve a practical or aesthetic
effect. Lighting includes the use of both
artificial light sources like lamps and light
fixtures, as well as natural illumination by
capturing daylight.
Power Distribution and Utilization 4
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Day lighting (using windows, skylights, or light
shelves) is sometimes used as the main source
of light during daytime in buildings. This can
save energy in place of using artificial lighting
Proper lighting can enhance task performance
improve the appearance of an area have positive psychological effects on
occupants
Power Distribution and Utilization 5
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Power Distribution and Utilization 6
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Indoor lighting is usually accomplished using light fixtures, andis a key part of interior design. Lighting can also be an intrinsic
component of landscape projects.
Power Distribution and Utilization 7
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Electrical LightingElectrical lighting has following advantages :
1. Cleanliness
2. Easy to control
3. Economical
4. Easy to handle
5. Steady output
6. Better reliability7. Suitable for almost all purposes etc.
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Terms used in Illumination1. Light
2. Luminous flux
3. Lumen
4. Plane angle
5. Solid angle
6. Steradian
7. Candle power8. Luminous intensity reduction factor
9. Glare
10.Lamp efficiency 9Power Distribution and Utilization
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light
That part of radiant energy from
a hot body which produced the
visual sensation on human eye iscalled light.
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Light and its PropertiesAll objects are emitting and
absorbing EM radia-tion. Consider a
poker placed in a fire.
As heating occurs, the emitted EMwaves have higher energy and
eventually become visible. First red . .
. then white.3
4
2
1
Lightmay be defined as electromagnetic radiation that is capable of
affecting the sense of sight.
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Electromagnetic Waves
c
E
B
Electric E
Magnetic B
Properties
1. Waves travel at the speed of
light c.
2. Perpendicular electric and
magnetic fields.
3. Require no medium forpropagation.3 x 10
8m/s
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The Wavelengths of LightThe electromagnetic spectrum spreads over a tremendous range of
frequencies or wavelengths. The wavelength is related to the frequencyf:
c = fl c = 3 x 108m/s
Those EM waves that are visible (light) have wave-lengths that range from
0.00004 to 0.00007 cm.
Red, l
0.00007 cm
Violet, l
0.00004 cm
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The EM SpectrumA wavelength of one nanometer
1 nm is:
1 nm = 1 x 10-9m
Red 700 nm Violet 400 nm
c = fl c = 3 x 108m/s
1024
1023
1022
1021
1020
1019
1018
1017
1016
1015
1014
1013
1012
1011
1010
109108
107
106
105
104
Frequency wavelengthf (Hz) l ( nm)
10-7
10-6
10-4
10-3
10-1
1
10
102103
104
105
106
107
108
109
1010
1011
1012
1013
Gamma rays
X-rays
Infrared rays
Short Radio
waves
Broadcast Radio
Long Radio
waves
Ultraviolet
400 nm700 nm
Visible Spectrum
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Example 1. Light from a Helium-Neon laser has a
wavelength of 632 nm. What is the frequency of this
wave?
8
-9
3 x 10 m/s
632 x 10 m
cc f fl
l
f = 4.75 x 1014 Hz Red light
The Helium Neon Laser Wavelength
l= 632 nm
Laser
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Properties of Light
Rectilinear propagation: Light travels in straight
lines. Reflection: Light striking a smooth surface turns
back into the original medium.
Refraction: Light bends when entering a transparent
medium.
Any study of the nature of light must explain the followingobserved properties:
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The Nature of Light
Physicists have studied light for centuries, finding that it sometimesbehaves as a particle and sometimes as a wave. Actually, both are
correct!
Reflection and rectilinear
propagation (straight line
path)
Dispersion of white
light into colors.
Reflection and Rectilinear
Propagation (straight line
path)
Dispersion of white light
into colors
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Photons and Light Rays
Light may be thought of as little bundles of waves emitted in discrete
packets called photons.
photons
The wave treatment uses raysto show the direction of
advancing wave fronts.
Light
ray
Light rays are
convenient fordescribing how light
behaves.
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Light Rays and Shadows
A geometric analysis may be made of shadows by tracing light raysfrom a point light source:
shadow
screen
Point
source
The dimensions of the shadow can be found by using geometry and
known distances.
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Example 2: The diameter of the ball is 4 cmand it is located 20
cmfrom the point light source. If the screen is 80 cmfrom the
source, what is the diameter of the shadow?
4 cm
20 cm
80 cm
h
The ratio of
shadow to the
source is same
as that of ball tosource. Therefore:
(4 cm)(80 cm)
20 cm
h h = 16 cm
4 cm
80 cm 20 cm
h
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The Sensitivity Curve
Sensitivity curve
Wavelength l
Sens
itivity
Human eyes are not equally
sensitive to all colors.
Eyes are most sensi- tive in
the mid-range near = 555nm.
555 nm
400 nm 700 nm
40 W 40 W
Yellowlight appears brighter to the eye than
does red light.
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Luminous Flux
Luminous fluxis the portion of total radiant power that is capable of
affecting the sense of sight.
Typically only about 10% of the power(flux) emitted from a light bulb falls in
the visible region.
The unit for luminous flux is the lumen.
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Lumen
It is the unit of luminous flux. One
lumen is defined as the luminous flux
emitted per unit solid angle from apoint source of one candle power.
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The Lumen as a Unit of FluxOne lumen (lm) is the luminous flux emitted from a 1/60 cm2opening in
a standard source and included in a solid angle of one steradian (1 sr).
In practice, sources of light are usually rated by comparison to a
commercially prepared standard light source.
A typical 100-Wincandescent light bulb emits a
total radiant power of about 1750 lm. This is forlight emitted in all directions.
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The Lumen in Power UnitsRecalling that luminous flux is really radiant power allows us to
define the lumen as follows:
One lumen is equal to 1/680 W of yellow-green light of
wavelength 555 nm.
Wavelength l
Sensitivity curveA disadvantage of this approach is
the need to refer to sensitivity curves
to determine the flux for different
colors of light.
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The angle subtended at a point by two converging lines lying in the same plane is
called plane angle. It is measured in radians and equal to the ratio of the length
of the arc to its radius,
= arc/ radius = l/ r radians
26Power Distribution and Utilization
Plane Angle
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The angle subtended by the partial surface area of a sphere at its centre is called
as solid angle. It is measured in steradians and equal to the ratio of area of the
surface to the square of radius of sphere,
= area of surface/ square of radius = A/ r
2
steradians 27Power Distribution and Utilization
Solid Angle
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Steradian
the unit of solid angle. One steradian is
defined as the solid angle that is
subtended at the centre of a sphere by
its surface having area equal to radius
square,
= surface area/ (radius)2
= r 2/ r2= 1 steradian
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Working with luminous flux requires the use of a solid angle measure called
the steradian (sr).
W
AR
The Steradian
2
A
RW
A solid angle of one steradian(1sr) is subtended at the center of
a sphere by an areaAequal to
the square of its radius ( R2 ).
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Example 3. What solid angle is subtended at the
center of a sphere by an area of 1.6 m2? The
radius of the sphere is 5 m.
W
A 1.6
m2
R 5
m
The Steradian
2A
RW
2
2
1.60 m
(5.00 m)W
2
A
R
W
W= 0.00640 sr
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Candle Power
The light radiating capacity of a source iscalled its candle power. The number of
lumens given out by a source per unit
solid angle in a given direction is calledits candle power. It is denoted by C.P.
Total flux emitted = CP X solid angle
= 1 X 4= 4 lumens
= 4lumens
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Luminous Intensity
Luminous intensity in any particulardirection is the luminous flux emitted by
the source per unit solid angle in that
direction. It is denoted by I and its unit is candela or
candle power (CP) .
Luminous intensity of source in a
particular direction, I = /
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Illumination
When light falls on a surface, it becomesvisible, the phenomenon is called as
illumination.
It is defined as luminous flux falling on asurface per unit area. It is denoted by E
and measured in lumen per square meter
or meter- candle.
E = / A lux
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Lux
One meter candle or lux is defined as the
illumination produced by a uniform
souce of one CP on the inner surface of asphere of radius one meter.
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GlareIn the human eye, the opening of pupil is controlled
by its iris which depends upon the intensity oflight received by the eye. If the eye is exposed to
a very bright source of light, the pupil of the eye
contracts automatically in order to reduce theamount of light admitted and prevent damage to
the retina. This effect is called glare.
Glare is defined as the brightness within the field of
vision of such a character so as to cause
discomfort and interference in vision.
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Lamp EfficiencyIt is defined as the visible radiations emitted
by it in lumens per watt.Usually, the light sources do not radiate
energy only in the visible spectrum. The
radiant energy is also accompanied with
infrared and ultra violet radiations.
Sun light produces majority of radiations inthe visible spectrum. The tungsten lamp
produces small radiations so its efficiency is
very poor.38Power Distribution and Utilization
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Lamp efficiency
The efficiency of fluorescent lamp is more than
tungsten lamp.
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Reflection Factor
Whole of the light incident on a reflecting
surface is not reflected. Some portion of it is
absorbed by the surface.
The ratio of the reflected light to the incident
light is called reflection factor.
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Law of Illumination
The illumination on a surface depends upon the
luminous intensity, distance between the
source and surface and the direction of rays of
light. It is governed by following laws :
1. Inverse square law
2. Lambertscosine law
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Inverse Square LawIt states that the illumination of a surface is inversely
proportional to the square of the distance of the surface from
the source. E 1/d242Power Distribution and Utilization
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Lamberts Cosine LawThis law states that the illumination on any surface is
proportional to the cosine of angle between the direction of the
incident flux and perpendicular to the area. E = 1/d2cos 43Power Distribution and Utilization
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THANKSEveryone wishes to go there . But no one wants to
buy the ticket . Heaven