Transcript Power Distribution & Utilization

Illumination Engineering
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Introduction
Terms Used in Illumination
Laws of Illumination
Photometry
Measurement of Illumination
Sources of Light
Arc Lamps
Incandescent Lamps
Basic Principles of Light Control
Types of Lighting Scheme
Design of Lighting Scheme
Factory Lighting
Street Lighting
Flood Lighting
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Light is the prime factor in human life.
All activities ultimately depend upon the light.
Artificial light is used in absence of natural
light.
Artificial light due to its cleanliness, ease of
control, reliability, steady output, low cost is
playing a great role in our lives.
Science of illumination engineering is,
therefore, becoming of major importance.
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Light is a form of radiant energy.
Depends on the temperature of bodies emitting
them.
Heat of the body can be classified as red hot or
white hot.
When the temperature increases, the body
changes from red hot to white hot.
Higher the temperature of the body, lower the
wavelength of radiant energy, and higher the
radiant efficiency.
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The sensation of color is due to the difference
in wavelengths of the light radiations.
Visible light can have a wavelength between
4,000Aº and 7,500Aº.
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Sensitivity of the eye to the lights of different
wavelengths varies from person to person and
according to the age.
Eye has greatest sensitivity for wavelengths of
about 5,500Aº
The relative sensitivity at any particular
wavelength λ is written as kλ and known as
relative luminosity factor.
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It differs from light very much.
Light is the cause and illumination is the result
of that light on surfaces on which it falls.
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Light: defined as radiant energy.
Luminous Flux: defined as total quantity of light
energy emitted per second from a luminous body.
Luminous Intensity: it is the luminous flux emitted by
the source per unit angle.
Lumen: it is the unit of luminous flux.
Candle Power: it is the light radiating capacity of the
source in a given direction. Denoted by CP.
Illumination: when light falls upon any surface, it is
called illumination.
Lux or Metre Candle: it is the unit of illumination.
Candela: it is the unit of luminous intensity.
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Mean Horizontal Candle Power (MHCP): it is the
mean of candle powers in all directions in
horizontal plane containing source of light.
Mean Spherical Candle Power (MSCP): it is the
mean of candle powers in all directions and in all
planes from source of light.
11. Mean Hemi-Spherical Candle Power
(MHSCP): it is the mean of candle powers in all
directions above or below the horizontal plane.
12. Reduction Factor:
MSCP/MHCP
13. Lamp Efficiency: ratio of luminous flux to the
power input.
1.
Law of Inverse Squares: if a source of light
which emits light equally in all directions be
placed at the centre of a hollow sphere, the
light will fall uniformly on the inner surface of
the sphere, that is to say, each square mm of
the surface will receive the same amount of
light.
2. Lambert’s Cosine Law:
The illumination at any point on a surface is
proportional to the cosine of the angle between
the normal at that point and the direction of
luminous flux.
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The candle power of a source in any given
direction is measured by comparison with a
standard or substandard source employing
photometer bench and some form of
photometer.
Photometer bench essentially consists of two
steel rods which carry the stands or saddles for
holding the two sources.
The principle of most of the methods of
measurement is based upon inverse square
law.
Most common type of photometers are:
1.
Bunsen Grease Spot Photometer: consists of a
piece of tissue paper with grease spot in the
centre.
2.
Flicker Photometer: used when two sources
giving light of different colors are to be
compared.
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The best method of measuring illumination is
by a portable type illumination photometer
calibrated to read directly in lux.
No shadow should be allowed to fall on the
meter during measurements.
Meter should be held perfectly horizontal and
stationary for accurate results.
Meter should be color corrected type so that it
can be used for all kinds of light sources.
Light sources may be grouped as:
1.
Arc Lamps
2.
High Temperature Lamps
3.
Gaseous Discharge Lamps
4.
Fluorescent Type Lamps
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In an arc lamp, electric current is made to flow
through two electrodes in contact with each
other which are drawn apart.
The result is an arc being struck.
The arc maintains the current and is very
sufficient source of light.
Its different types are:
Carbon Arc Lamp
Flame Arc Lamp
Magnetic Arc Lamp
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It consists of a glass globe completely evacuated and a
fine wire, known as filament, within it.
The glass globe is evacuated to prevent the oxidation
and convection currents of the filament and also to
prevent the temperature being lowered by radiation.
Material must possess the properties of high melting
point, low vapor pressure, high resistivity, low
temperature coefficient, ductility and sufficient
mechanical strength.
Carbon, osmium, tantalum and tungsten are used as
filament material.
Now a days, tungsten is the most commonly used
metal for filament due to its high melting point.
Average efficiency of tungsten filament is about 10
lumens per watt.
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When light falls on a surface, some portion of
the light is reflected, some portion is
transmitted through the medium of the surface
and the rest is absorbed.
The ratio of reflected light energy to the
incident light energy is known as reflection
factor.
There are two types of reflection:
Mirror or Specular Reflection
Diffuse Reflection
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In case of specular reflection, a beam of light is
reflected but not scattered and unless the eye is
placed in the path of reflected beam, viewer is
unaware of existence of light.
In diffuse reflection, reflected light is scattered
in all the directions.
A surface that is free from mirror reflection is
called mat surface.
It may be classified as:
1.
Direct Lighting: most commonly used. More than 90%
of total light flux is made to fall directly on working
plane.
2.
Semi-Direct Lighting: 60 to 90% of the total light flux
is made to fall downwards directly with the help of
semi-direct reflectors.
3.
Semi-Indirect Lighting: 60 to 90% of the total light
flux is thrown upwards to the ceiling for diffuse
reflection.
4. Indirect Lighting: 90% of the total light flux is
thrown upwards to the ceiling for diffuse
reflection by using inverted or bowl reflectors.
5. General Lighting: in this scheme, lamps made
of diffusing glass are used which give nearly
equal illumination in all directions.
The design of Lighting scheme should be such that
it may
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Provide adequate illumination.
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Provide light distribution all over the working
plane as uniform as possible.
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Provide light of suitable color.
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Avoid glare and hard shadows as far as
possible.
The following factors are required to be considered
while designing the Lighting scheme:
1.
Illumination Level.
2.
Uniformity of Illumination.
3.
Color of Light.
4.
Shadows.
5.
Glare.
6.
Mounting Height.
7.
Spacing of Luminaries.
8.
Color of Surrounding Walls.
Adequate Lighting of factories is of vital
importance.
It provides:
 Improved amenities for employees.
 Increased production.
 Reduce accidents.
 Prevents loss of time.
 Compensation payments.
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Main objectives of street Lighting are:
 To make the traffic and obstructions on the
road clearly visible.
 To make the street more attractive.
 To increase the community value of the street.
Direct Lighting scheme is employed as there are
no walls or ceiling which reflect or diffuse
light.
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It means flooding of large surfaces with light
from powerful projectors.
It is employed to serve the following purposes:
Aesthetic Flood Lighting: for enhancing
beauty of building at night.
Industrial and Commercial Flood Lighting:
for illuminating railway yards, sports
stadiums, construction sites etc.
Advertising: for illuminating advertisement
boards.
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