LECTURE 01 Illumination

8/12/2019 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.



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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.



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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



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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.



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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 sensitive 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


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

Documents

LECTURE 01 Illumination