Conclusions on Illumination Engineering - Module 4 Lighting Application Lesson 20 Notes | EduRev

: Conclusions on Illumination Engineering - Module 4 Lighting Application Lesson 20 Notes | EduRev

 Page 1


 
 
 
 
 
 
 
 
 
Module 
4 
 
Lighting Application 
Version 2 EE IIT, Kharagpur 1
Page 2


 
 
 
 
 
 
 
 
 
Module 
4 
 
Lighting Application 
Version 2 EE IIT, Kharagpur 1
 
 
 
 
 
 
 
 
 
Lesson 
20 
 
Conclusions on 
Illumination Engineering 
Version 2 EE IIT, Kharagpur 2
Page 3


 
 
 
 
 
 
 
 
 
Module 
4 
 
Lighting Application 
Version 2 EE IIT, Kharagpur 1
 
 
 
 
 
 
 
 
 
Lesson 
20 
 
Conclusions on 
Illumination Engineering 
Version 2 EE IIT, Kharagpur 2
This lesson is to conclude the first part of the course on Illumination Engg. 
 
             
             
             
             
             
             
             
             
             
             
 
            
 
 
 
It recaps the summary of material covered under Illumination Engineering. This forms the 50 % 
of the course. Nineteen lessons covered need for lighting, behavior of eye, Principles of artificial 
Lighting, Measurements, calculations & Applications. Figure 1 shows the typical inputs 
necessary to a person dealing with Illlumination Engg. to make it useful to the humanity. 
 
First lesson stressed the need for lighting .Good lighting aims so that our eyes clearly and 
pleasantly perceive things. Invariably artificial lighting schemes use some form of physical 
phenomena. All lighting sources today employ electrical energy. Electrical Energy sources may 
be DC or AC single phase or three phases. Usual Sources of electrical energy are Hydro & 
Thermal. Usually load is unbalanced for a practical 3-phase system. 
 
Radiation 
 
Second lesson deals with radiation.  Light is the Radiant energy that provides visual sensation.  
Human eye can sense over the 380nm (violet) to 700nm (red) wavelength.. Maximal relative 
energy content of sunlight around 550 nm coincident with maximal luminosity of human eye. 
Artificial light sources employed may be broadly categorized as Incandescent Lamps and Gas 
Discharge Lamps. These are based on the following four Physical Processes: 
 
• Incandescence 
• Luminescence 
• Fluorescence 
• Phosphorescence 
 
However, we learn as we go along that Good efficient lighting is obtained by combining 
luminescence & fluorescence. Having learnt about necessity of artificial Illumination and 
radiation characteristics, it is time to look at how the eye responds. 
     
 
 
 
Usefulness 
To 
Humanity 
Physiology 
Psychology
Math 
Chemistry
Physics 
Economics 
Art 
Illum
Engineerin
ination 
g 
(Aesthetic)
Fig. 1 Inputs necessary for Illumination Engg 
Version 2 EE IIT, Kharagpur 3
Page 4


 
 
 
 
 
 
 
 
 
Module 
4 
 
Lighting Application 
Version 2 EE IIT, Kharagpur 1
 
 
 
 
 
 
 
 
 
Lesson 
20 
 
Conclusions on 
Illumination Engineering 
Version 2 EE IIT, Kharagpur 2
This lesson is to conclude the first part of the course on Illumination Engg. 
 
             
             
             
             
             
             
             
             
             
             
 
            
 
 
 
It recaps the summary of material covered under Illumination Engineering. This forms the 50 % 
of the course. Nineteen lessons covered need for lighting, behavior of eye, Principles of artificial 
Lighting, Measurements, calculations & Applications. Figure 1 shows the typical inputs 
necessary to a person dealing with Illlumination Engg. to make it useful to the humanity. 
 
First lesson stressed the need for lighting .Good lighting aims so that our eyes clearly and 
pleasantly perceive things. Invariably artificial lighting schemes use some form of physical 
phenomena. All lighting sources today employ electrical energy. Electrical Energy sources may 
be DC or AC single phase or three phases. Usual Sources of electrical energy are Hydro & 
Thermal. Usually load is unbalanced for a practical 3-phase system. 
 
Radiation 
 
Second lesson deals with radiation.  Light is the Radiant energy that provides visual sensation.  
Human eye can sense over the 380nm (violet) to 700nm (red) wavelength.. Maximal relative 
energy content of sunlight around 550 nm coincident with maximal luminosity of human eye. 
Artificial light sources employed may be broadly categorized as Incandescent Lamps and Gas 
Discharge Lamps. These are based on the following four Physical Processes: 
 
• Incandescence 
• Luminescence 
• Fluorescence 
• Phosphorescence 
 
However, we learn as we go along that Good efficient lighting is obtained by combining 
luminescence & fluorescence. Having learnt about necessity of artificial Illumination and 
radiation characteristics, it is time to look at how the eye responds. 
     
 
 
 
Usefulness 
To 
Humanity 
Physiology 
Psychology
Math 
Chemistry
Physics 
Economics 
Art 
Illum
Engineerin
ination 
g 
(Aesthetic)
Fig. 1 Inputs necessary for Illumination Engg 
Version 2 EE IIT, Kharagpur 3
Eyes & Vision 
 
A human eye resembles a camera in structure and function. Important parts of a human eye are 
Iris / pupil,   Lens and Retina. The vision is either Photopic (dealing with fine image details and 
color discrimination, due to cone cells) or Scotopic (functions in dim light and no image details, 
due to rod cells). It may be mentioned that Human eye is achromatic in nature. Dispersive power 
of human eye is little greater than water. Eye is subject to Purkinjee Effect essentially dealing 
with shift of luminosity and ability of eye to adjust.  Best sensitivity of cone cells is around 
550nm (i.e. yellowish green hue) and that for rod cells is around 507nm (i.e.bluish green). Good 
lighting scheme should aim at Prevention of defective vision, Optimization of resources and 
improving conditions of visibility. Visibility depends on the (Observer Issues) size / details of 
object, level / quality of illumination, contrast / color and available time. It also depends on 
efficacy of individual, one’s eye defects, optical / physical fatigue and distraction. The Causes of 
fatigue could be rotating source, focusing on the source of glare, reading double impression. 
Usually after a days work pupil is dilated a nights rest offsets fatigue due to a days 
work.Visibility reduces due to eye defects and fatigues. Eye defects are caused due to aging, use 
or abuse. Hence, good illum0ination looks for producing clear and quick images. Illumination 
affects physiology as well as psychology, hence quality lighting is important. Factors governing 
illumination quality are glare, diffusion, direction / focus, composition and distribution. 
Minimum lighting required for good visibility is 100 ft-cd or more. For good visibility, 
brightness of surrounding should be greater than 0.01 ft-L & also should be less than that of the 
test object. Apart from illumination, visibility is talked in terms of visual acuity, visual efficacy, 
visual speed and visual health. 
Acuity is the ability to distinguish details depending upon: brightness of the object, 
characteristics of light entering the eye, contrast maintained. With age there is a reduction of 
visual activity, decrease in size & elasticity of pupil, decrease in flexibility of optic lens there by 
leading to higher levels of illumination requirement. Monochromatic light has good acuity 
producing distinct images on retina and details are distinguished well. Combination of different 
colors reduces acuity which is known as Chromatic Aberration. Color sensation by eye has a lag 
which depends on presentation & cessation of stimulus, rate of rise / fall of sensation (different 
for various colors) and nature of simultaneous colors & combination of colors 
 
Laws of Illumination  
 
Next lesson deals with quantification Illumination. Unit of luminous intensity is Candela (Cd), it 
is the luminous intensity of a surface which is1/600,000 of a blackbody, at the solidification 
temperature of Platinum (1773 °C) under standard atmospheric pressure. Luminous intensity 
over 1 steradian solid angle by a source of 1 Cd is called as 1 lumen of light flux (lm). For a 
point source one talks of MSLI or average intensity x solid angle (mean spherical Luminous 
intensity). Hence, Luminous Flux = luminous intensity × solid angle. Illuminance is luminous 
flux per unit area.                    
Frechner’s Law states that the same percentage change in stimulus calculated from the least 
amount perceptible gives the same change in sensation. Inverse Square Law states that the 
intensity of illumination produced by a point source varies inversely as square of the distance 
from the source.  
 
• Lambert’s Cosine Law of Incidence – 
2
I×cos a
E=
D
  
Version 2 EE IIT, Kharagpur 4
Page 5


 
 
 
 
 
 
 
 
 
Module 
4 
 
Lighting Application 
Version 2 EE IIT, Kharagpur 1
 
 
 
 
 
 
 
 
 
Lesson 
20 
 
Conclusions on 
Illumination Engineering 
Version 2 EE IIT, Kharagpur 2
This lesson is to conclude the first part of the course on Illumination Engg. 
 
             
             
             
             
             
             
             
             
             
             
 
            
 
 
 
It recaps the summary of material covered under Illumination Engineering. This forms the 50 % 
of the course. Nineteen lessons covered need for lighting, behavior of eye, Principles of artificial 
Lighting, Measurements, calculations & Applications. Figure 1 shows the typical inputs 
necessary to a person dealing with Illlumination Engg. to make it useful to the humanity. 
 
First lesson stressed the need for lighting .Good lighting aims so that our eyes clearly and 
pleasantly perceive things. Invariably artificial lighting schemes use some form of physical 
phenomena. All lighting sources today employ electrical energy. Electrical Energy sources may 
be DC or AC single phase or three phases. Usual Sources of electrical energy are Hydro & 
Thermal. Usually load is unbalanced for a practical 3-phase system. 
 
Radiation 
 
Second lesson deals with radiation.  Light is the Radiant energy that provides visual sensation.  
Human eye can sense over the 380nm (violet) to 700nm (red) wavelength.. Maximal relative 
energy content of sunlight around 550 nm coincident with maximal luminosity of human eye. 
Artificial light sources employed may be broadly categorized as Incandescent Lamps and Gas 
Discharge Lamps. These are based on the following four Physical Processes: 
 
• Incandescence 
• Luminescence 
• Fluorescence 
• Phosphorescence 
 
However, we learn as we go along that Good efficient lighting is obtained by combining 
luminescence & fluorescence. Having learnt about necessity of artificial Illumination and 
radiation characteristics, it is time to look at how the eye responds. 
     
 
 
 
Usefulness 
To 
Humanity 
Physiology 
Psychology
Math 
Chemistry
Physics 
Economics 
Art 
Illum
Engineerin
ination 
g 
(Aesthetic)
Fig. 1 Inputs necessary for Illumination Engg 
Version 2 EE IIT, Kharagpur 3
Eyes & Vision 
 
A human eye resembles a camera in structure and function. Important parts of a human eye are 
Iris / pupil,   Lens and Retina. The vision is either Photopic (dealing with fine image details and 
color discrimination, due to cone cells) or Scotopic (functions in dim light and no image details, 
due to rod cells). It may be mentioned that Human eye is achromatic in nature. Dispersive power 
of human eye is little greater than water. Eye is subject to Purkinjee Effect essentially dealing 
with shift of luminosity and ability of eye to adjust.  Best sensitivity of cone cells is around 
550nm (i.e. yellowish green hue) and that for rod cells is around 507nm (i.e.bluish green). Good 
lighting scheme should aim at Prevention of defective vision, Optimization of resources and 
improving conditions of visibility. Visibility depends on the (Observer Issues) size / details of 
object, level / quality of illumination, contrast / color and available time. It also depends on 
efficacy of individual, one’s eye defects, optical / physical fatigue and distraction. The Causes of 
fatigue could be rotating source, focusing on the source of glare, reading double impression. 
Usually after a days work pupil is dilated a nights rest offsets fatigue due to a days 
work.Visibility reduces due to eye defects and fatigues. Eye defects are caused due to aging, use 
or abuse. Hence, good illum0ination looks for producing clear and quick images. Illumination 
affects physiology as well as psychology, hence quality lighting is important. Factors governing 
illumination quality are glare, diffusion, direction / focus, composition and distribution. 
Minimum lighting required for good visibility is 100 ft-cd or more. For good visibility, 
brightness of surrounding should be greater than 0.01 ft-L & also should be less than that of the 
test object. Apart from illumination, visibility is talked in terms of visual acuity, visual efficacy, 
visual speed and visual health. 
Acuity is the ability to distinguish details depending upon: brightness of the object, 
characteristics of light entering the eye, contrast maintained. With age there is a reduction of 
visual activity, decrease in size & elasticity of pupil, decrease in flexibility of optic lens there by 
leading to higher levels of illumination requirement. Monochromatic light has good acuity 
producing distinct images on retina and details are distinguished well. Combination of different 
colors reduces acuity which is known as Chromatic Aberration. Color sensation by eye has a lag 
which depends on presentation & cessation of stimulus, rate of rise / fall of sensation (different 
for various colors) and nature of simultaneous colors & combination of colors 
 
Laws of Illumination  
 
Next lesson deals with quantification Illumination. Unit of luminous intensity is Candela (Cd), it 
is the luminous intensity of a surface which is1/600,000 of a blackbody, at the solidification 
temperature of Platinum (1773 °C) under standard atmospheric pressure. Luminous intensity 
over 1 steradian solid angle by a source of 1 Cd is called as 1 lumen of light flux (lm). For a 
point source one talks of MSLI or average intensity x solid angle (mean spherical Luminous 
intensity). Hence, Luminous Flux = luminous intensity × solid angle. Illuminance is luminous 
flux per unit area.                    
Frechner’s Law states that the same percentage change in stimulus calculated from the least 
amount perceptible gives the same change in sensation. Inverse Square Law states that the 
intensity of illumination produced by a point source varies inversely as square of the distance 
from the source.  
 
• Lambert’s Cosine Law of Incidence – 
2
I×cos a
E=
D
  
Version 2 EE IIT, Kharagpur 4
• Lambert’s Cosine law of Emission – 
   I
m
 = I × cos a 
 
Photometry 
 
The next lesson deals with Measurement issues. This is necessary before using any lamp source. 
This involves comparing it with a primary standard (standard lamp) using a photometric bench.  
This comparison may be carried out by varying position of standard lamp, by varying position of 
test lamp or by varying position of the screen on the photometric bench. The lesson also 
addresses issues pertaining to direction of light. Luminnaires are used for directing the light from 
a source of light in the desired direction. Types of luminaires employed may be broadly 
categorized as directed reflectors or   diffusing.    
   
Incandescent Lamps  
 
Having covered generics, we take now each type of lamp in the subsequent lessons. As the name 
suggests Incandescence employs radiation at high temperature. Incandescent Lamps called Type-
B employ tungsten / osmium / tantalum filament, in vacuum, where as those called Type-C: 
tungsten filament, in inert gas (generally a mixture of Ar & N
2
). Tungsten being ductile in 
nature, having high melting point & high radiation efficiency has been widely in use as filament 
material. However, at higher wattages the filament tends to evaporate and darken the bulb known 
as lamp darkening. Use of inert gas in incandescent lamps helps in decreasing the rate of 
evaporation of tungsten & improves efficiency. Further it is observed that higher efficiency is 
obtained when incandescent lamps are operated at low voltages. Filament characteristics depend 
on filament length, filament diameter, coil spacing, lead wires, method of mounting, no. of 
supports, properties of gas employed ,  gas pressure, bulb size and  shape of bulb. 
 
Usually Bulbs are designed for uniform radiation, accurate consumption of power, good 
efficiency and reasonable rating of life. The most common lamps employed fall under the 
category of Discharge Lamps, this is covered in the next three lessons. 
 
Discharge Lamps I  
 
This lesson introduces discharge lamps. They either use Luminescence which produces light 
radiation by chemical / electrical action on gas / vapor or Fluorescence where in radiation is 
absorbed at one wavelength & radiated at another wavelength with in visible spectrum. It is to be 
noted that in lighting arrangements a combination of luminescence & fluorescence increase 
efficiency far beyond incandescence. Efficiency is measured in terms of lumens per watt of 
power consumed. Thus discharge lamps consist of discharge of electricity through a tube 
containing a conducting medium. Conduction is by way of electrons. Types of electron emission 
may be Electric Field Emission, Thermionic Emission or Photoelectric Emission. So in a 
discharge lamp gas / vapor is made luminous by an electric discharge whose color / intensity are 
dependent on gas / vapor used and intensity to some extent proportional to current. Broadly 
discharge lamps are of two categories 1) Mercury Vapor Lamps, 2) Sodium Vapor Lamps. 
Mercury vapor lamps tend to give a light bluish green color (deficient in red color). They have a 
starting electrode provided to initiate the arc. After a run-up time of typically 2 min., mercury 
vapor discharge starts. Gas at high pressure improves the CRI (color rendering index) of mercury 
Version 2 EE IIT, Kharagpur 5
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