Illumination - Utilization of Electrical Energy | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE) PDF Download

 Page 1


      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
UNIT-1 
 
ILLUMINATION 
 
 
 
INTRODUCTION 
 
Study of illumination engineering is necessary not only to understand the principles of light 
control as applied to interior lighting design such as domestic and factory lighting but also 
to understand outdoor applications such as highway lighting and flood lighting. Now a day, 
the electrically produced light is preferred to the other source of illumination because of an 
account of its cleanliness, ease of control, steady light output, low cost, and reliability. The 
best illumination is that it produces no strain on the eyes. Apart from its esthetic and 
decorative aspects, good lighting has a strictly utilitarian value in reducing the fatigue of 
the workers, protecting their health, increasing production, etc.The science of illumination 
engineering is therefore becoming of major importance. 
 
NATURE OF LIGHT 
 
Light is a form of electromagnetic energy radiated from a body and human eye 
is capable of receiving it. Light is a prime factor in the human life as all activities of 
human being ultimately depend upon the light. 
Various forms of incandescent bodies are the sources of light and the light emitted 
by such bodies depends upon their temperature. A hot body about 500–800°C becomes a 
red hot and about 2,500–3,000°C the body becomes white hot. While the body is red hot, 
the wavelength of the radiated energy will be sufficiently large and the energy available in 
the form of heat. Further, the temperature increases, the body changes from red-hot to 
white-hot state, the wavelength of the radiated energy becomes smaller and enters into 
the range of the wavelength of light. The wavelength of the light waves varying from 
0.0004 to 0.00075 mm, i.e. 4,000-7,500 Å (1 Angstrom unit = 10–10 mm). The eye 
discriminates between different wavelengths in this range by the sensation of color. 
 
The whole of the energy radiated out is not useful for illumination purpose. 
Radiations of very short wavelength varying from 0.0000156 × 10–6m to 0.001 × 10–6 
m are not in the visible range are called as rontgen or x-rays, which are having the 
property of penetrating through opaque bodies. 
 
TERMS USED IN ILLUMINATION 
Page 2


      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
UNIT-1 
 
ILLUMINATION 
 
 
 
INTRODUCTION 
 
Study of illumination engineering is necessary not only to understand the principles of light 
control as applied to interior lighting design such as domestic and factory lighting but also 
to understand outdoor applications such as highway lighting and flood lighting. Now a day, 
the electrically produced light is preferred to the other source of illumination because of an 
account of its cleanliness, ease of control, steady light output, low cost, and reliability. The 
best illumination is that it produces no strain on the eyes. Apart from its esthetic and 
decorative aspects, good lighting has a strictly utilitarian value in reducing the fatigue of 
the workers, protecting their health, increasing production, etc.The science of illumination 
engineering is therefore becoming of major importance. 
 
NATURE OF LIGHT 
 
Light is a form of electromagnetic energy radiated from a body and human eye 
is capable of receiving it. Light is a prime factor in the human life as all activities of 
human being ultimately depend upon the light. 
Various forms of incandescent bodies are the sources of light and the light emitted 
by such bodies depends upon their temperature. A hot body about 500–800°C becomes a 
red hot and about 2,500–3,000°C the body becomes white hot. While the body is red hot, 
the wavelength of the radiated energy will be sufficiently large and the energy available in 
the form of heat. Further, the temperature increases, the body changes from red-hot to 
white-hot state, the wavelength of the radiated energy becomes smaller and enters into 
the range of the wavelength of light. The wavelength of the light waves varying from 
0.0004 to 0.00075 mm, i.e. 4,000-7,500 Å (1 Angstrom unit = 10–10 mm). The eye 
discriminates between different wavelengths in this range by the sensation of color. 
 
The whole of the energy radiated out is not useful for illumination purpose. 
Radiations of very short wavelength varying from 0.0000156 × 10–6m to 0.001 × 10–6 
m are not in the visible range are called as rontgen or x-rays, which are having the 
property of penetrating through opaque bodies. 
 
TERMS USED IN ILLUMINATION 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
The following terms are generally used in illumination. 
 
Color: The energy radiation of the heated body is monochromatic, i.e. the radiation of only one 
wavelength emits specific color. The wavelength of visible light lies between 4,000 and 7,500 
 
Å. The color of the radiation corresponding to the wavelength is 
shown in Fig. 6.1. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 6.1.Wavelength 
 
 
Relative sensitivity: The reacting power of the human eye to the light waves of different 
wavelengths varies from person to person, and also varies with age. The average relative 
sensitivity is shown in Fig. 6.2. The eye is most sensitive for a wavelength of 5,500 Å. So that, 
the relative sensitivity according to this wavelength is taken as unity. Referred from Fig. 6.1, 
blue and violet corresponding to the short wavelengths and red to the long wavelengths, 
orange, yellow, and green being in the middle of the visible region of wavelength. The color 
corresponding to 5,500 Å is not suitable for most of the applications since yellowish green. The 
relative sensitivity at any particular wavelength (?) is known as relative luminous factor (K?). 
 
 
 
 
 
 
 
 
 
 
 
Fig. 6.2 The average relative sensitivity 
Page 3


      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
UNIT-1 
 
ILLUMINATION 
 
 
 
INTRODUCTION 
 
Study of illumination engineering is necessary not only to understand the principles of light 
control as applied to interior lighting design such as domestic and factory lighting but also 
to understand outdoor applications such as highway lighting and flood lighting. Now a day, 
the electrically produced light is preferred to the other source of illumination because of an 
account of its cleanliness, ease of control, steady light output, low cost, and reliability. The 
best illumination is that it produces no strain on the eyes. Apart from its esthetic and 
decorative aspects, good lighting has a strictly utilitarian value in reducing the fatigue of 
the workers, protecting their health, increasing production, etc.The science of illumination 
engineering is therefore becoming of major importance. 
 
NATURE OF LIGHT 
 
Light is a form of electromagnetic energy radiated from a body and human eye 
is capable of receiving it. Light is a prime factor in the human life as all activities of 
human being ultimately depend upon the light. 
Various forms of incandescent bodies are the sources of light and the light emitted 
by such bodies depends upon their temperature. A hot body about 500–800°C becomes a 
red hot and about 2,500–3,000°C the body becomes white hot. While the body is red hot, 
the wavelength of the radiated energy will be sufficiently large and the energy available in 
the form of heat. Further, the temperature increases, the body changes from red-hot to 
white-hot state, the wavelength of the radiated energy becomes smaller and enters into 
the range of the wavelength of light. The wavelength of the light waves varying from 
0.0004 to 0.00075 mm, i.e. 4,000-7,500 Å (1 Angstrom unit = 10–10 mm). The eye 
discriminates between different wavelengths in this range by the sensation of color. 
 
The whole of the energy radiated out is not useful for illumination purpose. 
Radiations of very short wavelength varying from 0.0000156 × 10–6m to 0.001 × 10–6 
m are not in the visible range are called as rontgen or x-rays, which are having the 
property of penetrating through opaque bodies. 
 
TERMS USED IN ILLUMINATION 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
The following terms are generally used in illumination. 
 
Color: The energy radiation of the heated body is monochromatic, i.e. the radiation of only one 
wavelength emits specific color. The wavelength of visible light lies between 4,000 and 7,500 
 
Å. The color of the radiation corresponding to the wavelength is 
shown in Fig. 6.1. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 6.1.Wavelength 
 
 
Relative sensitivity: The reacting power of the human eye to the light waves of different 
wavelengths varies from person to person, and also varies with age. The average relative 
sensitivity is shown in Fig. 6.2. The eye is most sensitive for a wavelength of 5,500 Å. So that, 
the relative sensitivity according to this wavelength is taken as unity. Referred from Fig. 6.1, 
blue and violet corresponding to the short wavelengths and red to the long wavelengths, 
orange, yellow, and green being in the middle of the visible region of wavelength. The color 
corresponding to 5,500 Å is not suitable for most of the applications since yellowish green. The 
relative sensitivity at any particular wavelength (?) is known as relative luminous factor (K?). 
 
 
 
 
 
 
 
 
 
 
 
Fig. 6.2 The average relative sensitivity 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
Light: It is defined as the radiant energy from a hot body that produces the visual 
sensation upon the human eye. It is expressed in lumen-hours and it analogous to 
watthours,which denoted by the symbol ‘Q’. 
Luminous flux: It is defined as the energy in the form of light waves radiated per second 
from a luminous body. It is represented by the symbol ‘f’ and measured in lumens. 
 
Ex: Suppose the luminous body is an incandescent lamp. The total electrical power input to the 
lamp is not converted to luminous flux, some of the power lost through conduction, convection, and 
radiation, etc. Afraction of the remaining radiant flux is in the form of light waves lies in between 
the visual range of wavelength, i.e. between 4,000 and 7,000 Å, as shown in Fig. 6.3. 
 
 
 
 
 
 
 
 
Fig. 6.3 Flux diagram 
 
Radiant efficiency When an electric current is passed through a conductor, some 
heat is produced to I2R loss, which increases its temperature of the conductor. At low 
temperature, conductor radiates energy in the form of heat waves, but at very high 
temperatures, radiated energy will be in the form of light as well as heat waves. 
‘Radiant efficiency is defined as the ratio of energy radiated in the form of light, 
produces sensation of vision to the total energy radiated out by the luminous body’. 
 
 
 
 
 
 
 
Plane angle 
 
A plane angle is the angle subtended at a point in a plane by two converging lines 
(Fig.6.4). It is denoted by the Greek letter ‘?’ (theta) and is usually measured in 
degrees or radians. One radian is defined as the angle subtended by an arc of a circle 
whose length by an arc of a circle whose length is equals to the radius of the circle. 
Page 4


      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
UNIT-1 
 
ILLUMINATION 
 
 
 
INTRODUCTION 
 
Study of illumination engineering is necessary not only to understand the principles of light 
control as applied to interior lighting design such as domestic and factory lighting but also 
to understand outdoor applications such as highway lighting and flood lighting. Now a day, 
the electrically produced light is preferred to the other source of illumination because of an 
account of its cleanliness, ease of control, steady light output, low cost, and reliability. The 
best illumination is that it produces no strain on the eyes. Apart from its esthetic and 
decorative aspects, good lighting has a strictly utilitarian value in reducing the fatigue of 
the workers, protecting their health, increasing production, etc.The science of illumination 
engineering is therefore becoming of major importance. 
 
NATURE OF LIGHT 
 
Light is a form of electromagnetic energy radiated from a body and human eye 
is capable of receiving it. Light is a prime factor in the human life as all activities of 
human being ultimately depend upon the light. 
Various forms of incandescent bodies are the sources of light and the light emitted 
by such bodies depends upon their temperature. A hot body about 500–800°C becomes a 
red hot and about 2,500–3,000°C the body becomes white hot. While the body is red hot, 
the wavelength of the radiated energy will be sufficiently large and the energy available in 
the form of heat. Further, the temperature increases, the body changes from red-hot to 
white-hot state, the wavelength of the radiated energy becomes smaller and enters into 
the range of the wavelength of light. The wavelength of the light waves varying from 
0.0004 to 0.00075 mm, i.e. 4,000-7,500 Å (1 Angstrom unit = 10–10 mm). The eye 
discriminates between different wavelengths in this range by the sensation of color. 
 
The whole of the energy radiated out is not useful for illumination purpose. 
Radiations of very short wavelength varying from 0.0000156 × 10–6m to 0.001 × 10–6 
m are not in the visible range are called as rontgen or x-rays, which are having the 
property of penetrating through opaque bodies. 
 
TERMS USED IN ILLUMINATION 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
The following terms are generally used in illumination. 
 
Color: The energy radiation of the heated body is monochromatic, i.e. the radiation of only one 
wavelength emits specific color. The wavelength of visible light lies between 4,000 and 7,500 
 
Å. The color of the radiation corresponding to the wavelength is 
shown in Fig. 6.1. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 6.1.Wavelength 
 
 
Relative sensitivity: The reacting power of the human eye to the light waves of different 
wavelengths varies from person to person, and also varies with age. The average relative 
sensitivity is shown in Fig. 6.2. The eye is most sensitive for a wavelength of 5,500 Å. So that, 
the relative sensitivity according to this wavelength is taken as unity. Referred from Fig. 6.1, 
blue and violet corresponding to the short wavelengths and red to the long wavelengths, 
orange, yellow, and green being in the middle of the visible region of wavelength. The color 
corresponding to 5,500 Å is not suitable for most of the applications since yellowish green. The 
relative sensitivity at any particular wavelength (?) is known as relative luminous factor (K?). 
 
 
 
 
 
 
 
 
 
 
 
Fig. 6.2 The average relative sensitivity 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
Light: It is defined as the radiant energy from a hot body that produces the visual 
sensation upon the human eye. It is expressed in lumen-hours and it analogous to 
watthours,which denoted by the symbol ‘Q’. 
Luminous flux: It is defined as the energy in the form of light waves radiated per second 
from a luminous body. It is represented by the symbol ‘f’ and measured in lumens. 
 
Ex: Suppose the luminous body is an incandescent lamp. The total electrical power input to the 
lamp is not converted to luminous flux, some of the power lost through conduction, convection, and 
radiation, etc. Afraction of the remaining radiant flux is in the form of light waves lies in between 
the visual range of wavelength, i.e. between 4,000 and 7,000 Å, as shown in Fig. 6.3. 
 
 
 
 
 
 
 
 
Fig. 6.3 Flux diagram 
 
Radiant efficiency When an electric current is passed through a conductor, some 
heat is produced to I2R loss, which increases its temperature of the conductor. At low 
temperature, conductor radiates energy in the form of heat waves, but at very high 
temperatures, radiated energy will be in the form of light as well as heat waves. 
‘Radiant efficiency is defined as the ratio of energy radiated in the form of light, 
produces sensation of vision to the total energy radiated out by the luminous body’. 
 
 
 
 
 
 
 
Plane angle 
 
A plane angle is the angle subtended at a point in a plane by two converging lines 
(Fig.6.4). It is denoted by the Greek letter ‘?’ (theta) and is usually measured in 
degrees or radians. One radian is defined as the angle subtended by an arc of a circle 
whose length by an arc of a circle whose length is equals to the radius of the circle. 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
 
 
 
 
 
 
 
 
Fig. 6.4 Plane angle 
 
 
 
 
 
 
 
Solid angle Solid angle is the angle subtended at a point in space by an area, i.e., the 
angle enclosed in the volume formed by numerous lines lying on the surface and meeting 
at the point (Fig. 6.5). It is usually denoted by symbol ‘?’ and is measured in steradian. 
 
 
 
 
 
 
 
 
 
 
Fig.6.5 Solid angle 
 
 
 
 
 
The largest solid angle subtended at the center of a sphere: 
 
 
 
 
 
Relationship between plane angle and solid angle 
 
Let us consider a curved surface of a spherical segment ABC of height ‘h’ and radius 
of the sphere ‘r’ as shown in Fig. 6.6. The surface area of the curved surface of the 
spherical segment ABC = 2prh. From the Fig. 6.6: 
Page 5


      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
UNIT-1 
 
ILLUMINATION 
 
 
 
INTRODUCTION 
 
Study of illumination engineering is necessary not only to understand the principles of light 
control as applied to interior lighting design such as domestic and factory lighting but also 
to understand outdoor applications such as highway lighting and flood lighting. Now a day, 
the electrically produced light is preferred to the other source of illumination because of an 
account of its cleanliness, ease of control, steady light output, low cost, and reliability. The 
best illumination is that it produces no strain on the eyes. Apart from its esthetic and 
decorative aspects, good lighting has a strictly utilitarian value in reducing the fatigue of 
the workers, protecting their health, increasing production, etc.The science of illumination 
engineering is therefore becoming of major importance. 
 
NATURE OF LIGHT 
 
Light is a form of electromagnetic energy radiated from a body and human eye 
is capable of receiving it. Light is a prime factor in the human life as all activities of 
human being ultimately depend upon the light. 
Various forms of incandescent bodies are the sources of light and the light emitted 
by such bodies depends upon their temperature. A hot body about 500–800°C becomes a 
red hot and about 2,500–3,000°C the body becomes white hot. While the body is red hot, 
the wavelength of the radiated energy will be sufficiently large and the energy available in 
the form of heat. Further, the temperature increases, the body changes from red-hot to 
white-hot state, the wavelength of the radiated energy becomes smaller and enters into 
the range of the wavelength of light. The wavelength of the light waves varying from 
0.0004 to 0.00075 mm, i.e. 4,000-7,500 Å (1 Angstrom unit = 10–10 mm). The eye 
discriminates between different wavelengths in this range by the sensation of color. 
 
The whole of the energy radiated out is not useful for illumination purpose. 
Radiations of very short wavelength varying from 0.0000156 × 10–6m to 0.001 × 10–6 
m are not in the visible range are called as rontgen or x-rays, which are having the 
property of penetrating through opaque bodies. 
 
TERMS USED IN ILLUMINATION 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
The following terms are generally used in illumination. 
 
Color: The energy radiation of the heated body is monochromatic, i.e. the radiation of only one 
wavelength emits specific color. The wavelength of visible light lies between 4,000 and 7,500 
 
Å. The color of the radiation corresponding to the wavelength is 
shown in Fig. 6.1. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 6.1.Wavelength 
 
 
Relative sensitivity: The reacting power of the human eye to the light waves of different 
wavelengths varies from person to person, and also varies with age. The average relative 
sensitivity is shown in Fig. 6.2. The eye is most sensitive for a wavelength of 5,500 Å. So that, 
the relative sensitivity according to this wavelength is taken as unity. Referred from Fig. 6.1, 
blue and violet corresponding to the short wavelengths and red to the long wavelengths, 
orange, yellow, and green being in the middle of the visible region of wavelength. The color 
corresponding to 5,500 Å is not suitable for most of the applications since yellowish green. The 
relative sensitivity at any particular wavelength (?) is known as relative luminous factor (K?). 
 
 
 
 
 
 
 
 
 
 
 
Fig. 6.2 The average relative sensitivity 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
Light: It is defined as the radiant energy from a hot body that produces the visual 
sensation upon the human eye. It is expressed in lumen-hours and it analogous to 
watthours,which denoted by the symbol ‘Q’. 
Luminous flux: It is defined as the energy in the form of light waves radiated per second 
from a luminous body. It is represented by the symbol ‘f’ and measured in lumens. 
 
Ex: Suppose the luminous body is an incandescent lamp. The total electrical power input to the 
lamp is not converted to luminous flux, some of the power lost through conduction, convection, and 
radiation, etc. Afraction of the remaining radiant flux is in the form of light waves lies in between 
the visual range of wavelength, i.e. between 4,000 and 7,000 Å, as shown in Fig. 6.3. 
 
 
 
 
 
 
 
 
Fig. 6.3 Flux diagram 
 
Radiant efficiency When an electric current is passed through a conductor, some 
heat is produced to I2R loss, which increases its temperature of the conductor. At low 
temperature, conductor radiates energy in the form of heat waves, but at very high 
temperatures, radiated energy will be in the form of light as well as heat waves. 
‘Radiant efficiency is defined as the ratio of energy radiated in the form of light, 
produces sensation of vision to the total energy radiated out by the luminous body’. 
 
 
 
 
 
 
 
Plane angle 
 
A plane angle is the angle subtended at a point in a plane by two converging lines 
(Fig.6.4). It is denoted by the Greek letter ‘?’ (theta) and is usually measured in 
degrees or radians. One radian is defined as the angle subtended by an arc of a circle 
whose length by an arc of a circle whose length is equals to the radius of the circle. 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
 
 
 
 
 
 
 
 
Fig. 6.4 Plane angle 
 
 
 
 
 
 
 
Solid angle Solid angle is the angle subtended at a point in space by an area, i.e., the 
angle enclosed in the volume formed by numerous lines lying on the surface and meeting 
at the point (Fig. 6.5). It is usually denoted by symbol ‘?’ and is measured in steradian. 
 
 
 
 
 
 
 
 
 
 
Fig.6.5 Solid angle 
 
 
 
 
 
The largest solid angle subtended at the center of a sphere: 
 
 
 
 
 
Relationship between plane angle and solid angle 
 
Let us consider a curved surface of a spherical segment ABC of height ‘h’ and radius 
of the sphere ‘r’ as shown in Fig. 6.6. The surface area of the curved surface of the 
spherical segment ABC = 2prh. From the Fig. 6.6: 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig.6.6 Sectional view for solid angle 
 
 
 
 
 
BD = OB – OD From 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
From the Equation (6.3), the curve shows the variation of solid angle with plane 
angle is shown in Fig. 6.7.