2. Introduction
As we know that almost all human activities depends on light. Sun is
a prime natural source of light but artificial lighting plays almost
main role in our daily life. These artificial lights are produced by
mechanical lamps and electrical lamps.
But due to poor performance the mechanical light are totally
replaced by electrical lights. The electrical lighting are mainly
used for decorative purpose, advertising, traffic control , medical
field and street lighting etc.
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3. Electrical Lighting
Electrical lighting has following advantages :
1. Cleanliness
2. Easy to control
3. Economical
4. Easy to handle
5. Steady output
6. Better reliability
7. Suitable for almost all purposes etc.
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4. Sensitivity of Human Eye
As we know natural light consists of seven colors having different
wavelengths. The average human eye is most sensitive to a
wave length of 5500 0A.
The relative sensitivity of eye for a particular wave length is the
visual effect produced by the light on the average human eye
as compared with the effect of light having wave length 5500
0A on human eye.
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5. Sensitivity of Human eye
This is also known as Relative luminosity Factor.
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8. light
• That part of radiant energy from a hot body
which produced the visual sensation on
human eye is called light.
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9. Luminous Flux
• The total quantity of radiant energy per
second responsible for visual sensation from
a luminous body is called Luminous Flux.
• It is represented as F of Ø and measured in
lumens.
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10. Lumen
• It is the unit of luminous flux. One lumen is
defined as the luminous flux emitted per unit solid
angle from a point source of one candle power.
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11. Plane Angle
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 too its radius,
θ = arc/ radius = l/ r radians
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12. Solid Angle
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,
ω = area of surface/ square of radius = A/ r2 steradians
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13. 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,
ω = surface area/ (radius)2
= r 2 / r2 = 1 steradian
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14. Candle Power
• The light radiating capacity of a source is called its
candle power. The number of lumens given out by a
source per unit solid angle in a given direction is called
its candle power. It is denoted by C.P.
Total flux emitted = CP X solid angle
= 1 X 4π = 4π lumens
= 4π lumens
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15. Luminous Intensity
• Luminous intensity in any particular direction 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
= φ / ω
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17. light
• That part of radiant energy from a hot body
which produced the visual sensation on
human eye is called light.
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18. Luminous Flux
• The total quantity of radiant energy per
second responsible for visual sensation from
a luminous body is called Luminous Flux.
• It is represented as F of Ø and measured in
lumens.
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19. Lumen
• It is the unit of luminous flux. One lumen is
defined as the luminous flux emitted per unit solid
angle from a point source of one candle power.
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20. Plane Angle
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 too its radius,
θ = arc/ radius = l/ r radians
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21. Solid Angle
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,
ω = area of surface/ square of radius = A/ r2 steradians
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22. 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,
ω = surface area/ (radius)2
= r 2 / r2 = 1 steradian
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23. Candle Power
• The light radiating capacity of a source is called its
candle power. The number of lumens given out by a
source per unit solid angle in a given direction is called
its candle power. It is denoted by C.P.
Total flux emitted = CP X solid angle
= 1 X 4π = 4π lumens
= 4π lumens
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24. Luminous Intensity
• Luminous intensity in any particular direction 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
= φ / ω
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25. Illumination
When light falls on a surface, it becomes visible, the
phenomenon is called as illumination.
It is defined as luminous flux falling on a surface per unit
area. It is denoted by E and measured in lumen per
square meter or meter- candle.
E = Ф / A lux
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26. Lux
One meter candle or lux is defined as the illumination
produced by a uniform souce of one CP on the inner
surface of a sphere of radius one meter.
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27. Lamp Efficiency
It 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 in the visible
spectrum. The tungsten lamp produces small radiations so
its efficiency is very poor.
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29. Glare
In the human eye, the opening of pupil is controlled by its iris which
depends upon the intensity of light 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 the amount 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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30. How is Light Produced?
Methods of Light Production
31. Luminous:
An object which produces visible light
Ex: candle, sun, flashlight, neon lights
Non-luminous:
An object which does not produce visible
light; reflects or allows light to pass
through allow us to see the object
Moon, stained glass windows, coloured
liquids, textbook, pen, etc.
32. Electrical method of producing Light
Following are the methods of producing light :
1. By developing arc between two electrodes
2. By passing a current through a filament
3. By electric discharge through vapors or gases
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33. Methods of Light Production
• Incandescence:
– Production of light as a result of high temperature
– Ex: Candle, incandescent light bulb
35. How does an incandescent light bulb work?
The light bulb produces light when the fine coil of tungsten (called
a filament) is heated
Temperature rises to ~2500°C when an electric current passes through it!
Tungsten is used because other metals at this high of a temperature melts
Incandescent lamps are very inefficient sources of light because
most energy is lost as heat
Filled with a non-reactive gas because a more reactive gas could
combust
36. • Fluorescence:
– Immediate emission of visible light as a result of absorption of
ultraviolet light
– Ex: fluorescent lights
37. How does a fluorescent light bulb work?
1. A long cylindrical glass tube is filled with mercury vapour
2. Electrical current flows through the tube, from the electrode
which donates electrons to the electrode which accepts electrons
3. As the current flows through the tube, it excites atoms of mercury
4. The excited mercury atoms produce ultraviolet light (which we
cannot see)
5. The UV light strikes the fluorescent coating on the inside of the
glass tube and releases visible light
38. How does a fluorescent light bulb work?
Electrical
contact
Electron
discharge
Glass tubing
Fluorescent coating
Mercury (Hg)
atoms
Electrode
(electron donor )
Electrode
(electron
acceptor)
Visible light produced
39. • Electric discharge:
– Production of light by passing an electric current through a gas
– Aurora borealis, lightning, neon signs
40. • Phosphorescence:
– Production of light by absorbing UV light and emitting visible light
over an extended period of time
– Ex: glow in the dark stickers which contain phosphors
41. Lighting Schemes
Lighting schemes are classified according to the location,
requirement and purpose etc. are as under :
1. Direct lighting
2. Indirect lighting
3. Semi direct lighting
4. Semi indirect lighting
5. General lighting
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42. Direct Lighting
As is clear from the name, in this system almost 90 to 95 %
light falls directly on the object or the surface. The light is
made to fall upon the surface with the help of deep
reflectors. Such type of lighting scheme is most used in
industries and commercial lighting. Although this scheme is
most efficient but it is liable to cause glare and shadows.
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43.
44. Indirect Lighting
In this system, the light does not fall directly on the surface but
more than 90 % of light is directed upwards by using
diffusing reflectors. Here the ceiling acts as a source of light
and this light is uniformly distributed over the surface and
glare is reduced to minimum. It provides shadow less
illumination which is useful for drawing offices and
composing rooms. It is also used for decoration purposes in
cinema halls, hotels etc.
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45.
46. Semi direct Lighting
This is also an efficient system of lighting and chances of glare are
also reduced. Here transparent type shades are used through
which about 60 % light is directed downward and 40 % is
directed upward. This also provides a uniform distribution of
light and is best suited for room with high ceilings.
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47. Semi indirect Lighting
In this system about 60 to 90 % of total light is thrown upward to
the ceiling for diffused reflection and the rest reaches the
working plane directly. A very small amount of light is absorbed
by the bowl. It is mainly used for interior decoration.
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49. General Lighting
This system employs such type of luminaries, shades and
reflectors which give equal illumination in all the directions.
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50. 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. Lambert’s cosine law
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51. Inverse Square Law
It states that the illumination of a surface is inversely proportional to the square of the
distance of the surface from the source. E α 1/d2
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52. Lambert’s Cosine Law
This 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/d2 cos θ
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53. Factors required for Light Scheme
The following factors are required to be considered while
designing the lighting scheme :
1. Illumination level
2. Quality of light
3. Co efficient of utilization
4. Depreciation factor
5. Space height ratio
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54. Illumination Level
This is the most vital factor in deciding the number and wattage of
luminaries so that we are able to see and recognize the object
properly. Colors of the body have the property of reflecting the
light in different proportions, degree of illumination, its
distance from the viewer, contrast between the object to be
seen and its surroundings.
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55. Illumination Level
Type of work recommended illumination level
Offices 100-400 lumens/ meter square
Schools 250-400 lumens/ meter square
Industry 1000 lumens/ meter square
Shops 250-500 lumens/ meter square
Hotels 80-100 lumens/ meter square
Hospitals 250-3500 lumens/ meter square
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56. Quality of Light
This means that the illumination should not be harmful to the
viewers. It should be glare free, shadow less and contrast free.
Direct glare from the source of light is most common factor.
Presence of polished and glassy surface will cause indirect glare
unless diffused light is used. Hard and long shadows can be
avoided by using a large number of lamps and adjusting the
mounting height.
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57. Co – efficient of Utilization
A surface to be illuminated receive light either directly from the
lamps or reflected from the ceiling and walls or both. In this
case, the total flux reaching the surface will never be equal to
the flux emitted by the lamp, due to absorption by reflectors,
ceiling and walls.
Utilization factor = lumens reaching at the working place
total lumens emitted by the source
Usually it varies from 0.5 to 0.8.
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58. Depreciation Factor
The total flux emitted by the source and its fitting may be reduced
due to deposition of dust upon the surfaces. Similarly quantity
of light reflected from the ceiling and walls also decreases with
the passage of time. This is called as depreciation facto.
Usually it varies from 1.3 to 1.6.
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59. Space Height Ratio
The ratio of space (horizontal distance ) between the two adjacent
lamps to the vertical height of the lamps above the working
plane is called space height ratio.
So the distance between the lamps is not too much. An ideal
scheme could be when there is large number of small size
lamps are used also it increases the cost of installation. So the
space height ratio is 1 to 1.5.
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60. Space Height Ratio
The ratio of space (horizontal distance ) between the two adjacent
lamps to the vertical height of the lamps above the working
plane is called space height ratio.
So the distance between the lamps is not too much. An ideal
scheme could be when there is large number of small size
lamps are used also it increases the cost of installation. So the
space height ratio is 1 to 1.5.
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64. WHAT IS ELECTRIC HEATING ?
WHAT IS THE PRINCIPLE BEHIND IT ?
Electric heating is any process in which ELECTRICAL
ENERGY is converted to
“HEAT ENERGY”.
Electric heating works on the principle of ”JOULE
HEATING” (an electric current through a resistor
converts electrical energy into heat energy.)
65. INTRODUCTION
Electrical heating is based on the principle of that
when electric current passes through a medium heat is produced.
Let us take the case of solid material which as resistance ‘R’ ohms
and current flowing through it is I amps for ‘t’ seconds than heat
produced in the material will be H=I²Rt Joules.
66. • Modes of heating:
a) Conduction
b) Convection
c) Radiation
67. • REQUIREMENTS OF HEATING:
• It should have;
a. High specific resistance
b. High melting point
c. Should not oxidize at electrode temperature
d. Should not low temperature coefficient
e. Positive temperature coefficient
f. High ductility and flexibility
g. High mechanical strength
69. • Applications:
1. DOMESTIC PURPOSE:
• Hot plates for cooking
• Room heaters
• Immersion heaters for water
heating
• Electric irons
• Electric toasters
• Electric ovens for baking etc.
2. INDUSTRIAL PURPOSES:
• Melting of metals
• Moulding of glass
• Heat treatment
processes
• Baking of
insulators
• Enamelling of copper
wires etc.
70. • Advantages of heating:
1. Cleanliness
2. Absence of flue gases
3. Ease of control
4. Better working conditions
5. Ease of adaption
6. Very high efficiency of utilization
7. Uniform heating
8. Heating of non-conducting materials
9. Cheap furnaces
10. Nolimit to upper maximum temperature
71. CLASSIFICATION OF ELECTRIC HEATING
Power Frequency Heating
Resistance heating
o Direct resistance heating
o Indirect resistance heating
Arc heating
o Direct arc heating
o Indirect arc heating
High Frequency Heating
Induction heating
o Direct core type
o Core less type
Dielectric heating
72. POWER FREQUENCY HEATING
In this method, electrical power is directly utilised to heat substance i.e.,
standard frequency of the power supply is used to heat the substance.
RESISTANCE HEATING
In these method heating is done using the Ohmic loss in a highly
resistive heating element. Ohmic losses cause the conversion of
electrical energy into heat. This may be direct or indirect.
73. .
Direct Resistance Heating
In direct resistance heating, the substance to be heated is the heating element itself.
The flow of current offers a stirring action.
Indirect Resistance Heating
In indirect resistance heating, heat is conducted and radiated from the heating
element to the substance to be heated.
74. ARC HEATING
⚫ Arc heating utilizes the energy of electric arc to heat substances.
⚫ In direct arc heating, the substance to be heated acts as an electrode for the
formation of arc and is heated through direct contact with thearc.
⚫In indirect arc heating, heat is radiated from the arc between two sets of
electrodes to the heating substance.
Fig- DirectArc Heating Fig- IndirectArc Heating
75. HIGH FREQUENCY HEATING
It is a thermal process of heating , which is used to eliminate microorganisms.
This provide the rapid and uniform heat distribution and therefore minimize quality
reduction of products.
TYPES OF HIGH FREQUENCY HEATING:
1) Induction heating
a) Direct core types
b) Core less type
2) Dielectric heating
76. INDUCTION HEATING
It is heating of electrical conducting object generally metals by
electromagnetic induction.
Eddycurrent are generated within metal and due to resistance of
object lead to joule heating of metals.
Fig- Induction Heating
77. . Direct Core Type: The direct core furnace is essentially a transformer in which charge to be heated
forms the secondary this is designed for low frequency.
Core Less Type: No core is provided to core less induction furnace. A crucible of more convenient
shape can be employed. For coreless induction furnace power is obtained from ordinary supply system
and its frequency is converted to the higher value by means of oscillators.
Fig: Direct Core Type Fig: Core Less Type
78. DIELECTRIC HEATING
It is also is also known as electronic heating.
Radio frequency heating, and high-frequency heating, is the process in which a
radio frequency (RF) alternating electric field, or radio wave or microwave
electromagnetic radiation heats adielectric material.
Dielectric polarized by an applied electric field, when a dielectric is placed
in an electric field.
Fig: Dielectric Heating
79.
80. Electrical Lighting
Electrical lighting has following advantages :
1. Cleanliness
2. Easy to control
3. Economical
4. Easy to handle
5. Steady output
6. Better reliability
7. Suitable for almost all purposes etc.
11/03/2013
81. Sensitivity of Human Eye
As we know natural light consists of seven colors having different
wavelengths. The average human eye is most sensitive to a
wave length of 5500 0A.
The relative sensitivity of eye for a particular wave length is the
visual effect produced by the light on the average human eye
as compared with the effect of light having wave length 5500
0A on human eye.
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82. Sensitivity of Human eye
This is also known as Relative luminosity Factor.
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85. Plane Angle
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 too its radius,
θ = arc/ radius = l/ r radians
11/03/2013
86. Solid Angle
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,
ω = area of surface/ square of radius = A/ r2 = 4π steradians
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87. light
• That part of radiant energy from a hot body
which produced the visual sensation on
human eye is called light.it is denoted by
letter Q and units is lumens-hr
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98. Luminous:
An object which produces visible light
Ex: candle, sun, flashlight, neon lights
Non-luminous:
An object which does not produce visible
light; reflects or allows light to pass
through allow us to see the object
Moon, stained glass windows, coloured
liquids, textbook, pen, etc.
99. Electrical method of producing Light
Following are the methods of producing light :
1. By developing arc between two electrodes
2. By passing a current through a filament
3. By electric discharge through vapors or gases
11/03/2013
106. How does an incandescent light bulb work?
The light bulb produces light when the fine coil of tungsten (called
a filament) is heated
Temperature rises to ~2500°C when an electric current passes through it!
Tungsten is used because other metals at this high of a temperature melts
Incandescent lamps are very inefficient sources of light because
most energy is lost as heat
Filled with a non-reactive gas because a more reactive gas could
combust
107. • Fluorescence:
– Immediate emission of visible light as a result of absorption of
ultraviolet light
– Ex: fluorescent lights
108. How does a fluorescent light bulb work?
1. A long cylindrical glass tube is filled with mercury vapour
2. Electrical current flows through the tube, from the electrode
which donates electrons to the electrode which accepts electrons
3. As the current flows through the tube, it excites atoms of mercury
4. The excited mercury atoms produce ultraviolet light (which we
cannot see)
5. The UV light strikes the fluorescent coating on the inside of the
glass tube and releases visible light
109. How does a fluorescent light bulb work?
Electrical
contact
Electron
discharge
Glass tubing
Fluorescent coating
Mercury (Hg)
atoms
Electrode
(electron donor )
Electrode
(electron
acceptor)
Visible light produced
110. • Phosphorescence:
– Production of light by absorbing UV light and emitting visible light
over an extended period of time
– Ex: glow in the dark stickers which contain phosphors
111. Glare
In the human eye, the opening of pupil is controlled by its iris which
depends upon the intensity of light 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 the amount 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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112. TYPES OF GLARE
• DIRECT GLARE
• INDIRECT GLARE
• How to reduce glare
By increasing the height of lamp
By using reflectors
113. REQUIREMENTS OF GOOD LIGHTING
• ILLUMINATION LEVEL
1. Size of the object
2. State of object
3. Contrast between object and back ground.
• UNIFORMITY OF ILLUMINATION
• ABSENCE OF GLARE
• COLOUR OF LIGHT
• ELIMINATION OF SHADOWS
• CONTRAST
117. Lighting Schemes
Lighting schemes are classified according to the location,
requirement and purpose etc. are as under :
1. Direct lighting
2. Indirect lighting
3. Semi direct lighting
4. Semi indirect lighting
5. General lighting
11/03/2013
118. Direct Lighting
As is clear from the name, in this system almost 90 to 95 %
light falls directly on the object or the surface. The light is
made to fall upon the surface with the help of deep
reflectors. Such type of lighting scheme is most used in
industries and commercial lighting. Although this scheme is
most efficient but it is liable to cause glare and shadows.
11/03/2013
119.
120. Indirect Lighting
In this system, the light does not fall directly on the surface but
more than 90 % of light is directed upwards by using
diffusing reflectors. Here the ceiling acts as a source of light
and this light is uniformly distributed over the surface and
glare is reduced to minimum. It provides shadow less
illumination which is useful for drawing offices and
composing rooms. It is also used for decoration purposes in
cinema halls, hotels etc.
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121.
122. Semi direct Lighting
This is also an efficient system of lighting and chances of glare are
also reduced. Here transparent type shades are used through
which about 60 % light is directed downward and 40 % is
directed upward. This also provides a uniform distribution of
light and is best suited for room with high ceilings.
11/03/2013
123. Semi indirect Lighting
In this system about 60 to 90 % of total light is thrown upward to
the ceiling for diffused reflection and the rest reaches the
working plane directly. A very small amount of light is absorbed
by the bowl. It is mainly used for interior decoration.
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124.
125. General Lighting
This system employs such type of luminaries, shades and
reflectors which give equal illumination in all the directions.
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126.
127. There are 5 systems of artificial lighting:
1. DIRECT LIGHTING: 99-100 % of light is directed towards the
working area.
2. SEMI-DIRECT: 10 – 40 % of the light is projected upwards.
3. INDIRECT: 99 – 100 % of the light is directed towards the
roof.
4. SEMI-INDIRECT: Here 60 – 90 % of the light is directed
upwards and the rest downwards.
5. DIRECT –INDIRECT: Here the light is directed equally upwards and
downwards.
128. 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. Lambert’s cosine law
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129. Inverse Square Law
It states that the illumination of a surface is inversely proportional to the square of the
distance of the surface from the source. E α 1/d2
11/03/2013
130. Lambert’s Cosine Law
This 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/d2 cos θ
11/03/2013
131. Factors required for Light Scheme
The following factors are required to be considered while
designing the lighting scheme :
1. Illumination level
2. Quality of light
3. Co efficient of utilization
4. Depreciation factor
5. Space height ratio
11/03/2013
132. Illumination Level
This is the most vital factor in deciding the number and wattage of
luminaries so that we are able to see and recognize the object
properly. Colors of the body have the property of reflecting the
light in different proportions, degree of illumination, its
distance from the viewer, contrast between the object to be
seen and its surroundings.
11/03/2013
133. Illumination Level
Type of work recommended illumination level
Offices 100-400 lumens/ meter square
Schools 250-400 lumens/ meter square
Industry 1000 lumens/ meter square
Shops 250-500 lumens/ meter square
Hotels 80-100 lumens/ meter square
Hospitals 250-3500 lumens/ meter square
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134. Quality of Light
This means that the illumination should not be harmful to the
viewers. It should be glare free, shadow less and contrast free.
Direct glare from the source of light is most common factor.
Presence of polished and glassy surface will cause indirect glare
unless diffused light is used. Hard and long shadows can be
avoided by using a large number of lamps and adjusting the
mounting height.
11/03/2013
135. Co – efficient of Utilization
A surface to be illuminated receive light either directly from the
lamps or reflected from the ceiling and walls or both. In this
case, the total flux reaching the surface will never be equal to
the flux emitted by the lamp, due to absorption by reflectors,
ceiling and walls.
Utilization factor = lumens reaching at the working place
total lumens emitted by the source
Usually it varies from 0.5 to 0.8.
11/03/2013
