Illumination.ppt

UNIT-1
Illumination
Introduction, nature and production of light, Sensitivity of
the eye, Units of light. The inverse square law and cosine
law, Solid angle, lighting calculations, determination of
M.S.C.P, Rousseau’s construction, Discharge lamps,
Sodium vapour lamps, Mercury vapour lamps, Fluorescent
lamps, Starting and power factor corrections, Stroboscopic
effects, Neon signs, Application to factory lighting, Street
lighting and Flood lighting.

Topics
1. Introduction
2. Nature of light
3. Terms used in illumination
4. Law of illumination
5. Electrical methods of producing light
6. Sources of light
7. Arc lamps
8. Filament lamps
9. Gaseous discharge lamps

Topics
10. Sodium vapor lamp
11. Mercury vapor lamp
12. Fluorescent tube
13. Neon lamp
14. Halogen lamp
15. Compact fluorescent lamp
16. Candle power and its measurement
17. Lighting scheme
18. Street light
19. Flood lighting

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.

Increase in temperature produces an increase in the amount of both
kinds of radiations(heat and light) but the colour of light or visible
radiation changes from bright red to orange, to yellow and then finally,
if the temperature is high enough, to white. As temperature is
increased, the wavelength of the visible radiation goes on becoming
shorter. It should be noted that heat waves are identical to light waves
except that they are of longer wavelength and hence produce no
impression on the retina. Obviously, from the point of view of light
emission, heat energy represents so much wasted energy.

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.

7
Color
Temperature
Scale
Cool White - 4100K
Daylight Fluo - 6500K
North Sky - 8500K
Warm White - 3000K
HPS - 2100K
Halogen – 3100K
Incandescent – 2700K

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.

Sensitivity of
Human eye
This is also
known as
Relative
luminosity
Factor.

Terms used in Illumination
1. Light
2. Luminous flux
3. Lumen
4. Plane angle
5. Solid angle
6. Steradian
7. Candle power
8. Luminous intensity reduction factor
9. Glare
10. Lamp efficiency

light
•That part of radiant energy from
a hot body which produced the
visual sensation on human eye is
called light.

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.

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.

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

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

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

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

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

Reduction Factor
reduction factor of a source of light is the
ratio of its mean spherical candle power
to its mean horizontal candle power.
Reduction factor = MSCP/ MHCP

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

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.

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.

Efficiency
• Lighting efficiency is expressed as lumens
output/wattage input.
• Ranges from 4 to 150 lumens/watt.

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.

Lamp efficiency
The efficiency of fluorescent lamp is more than
tungsten lamp.

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.

Laws 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

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

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

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

Arc Lamp
The principle of an arc lamp is that when two
electrodes carrying current are separated through a
small distance, an arc is struck between them. The arc
lamps were used in the past for street lighting
purposes but now a days these are used when
extreme brightness is required.
Most commonly use arc lamp is
Carbon Arc Lamp

Carbon Arc Lamp
This is the oldest type of lamp and is still being
employed in cinema projectors and search lights. It
consists of two hard carbon rods (Electrodes).
The diameter of +ve electrode is double to that of –ve
electrode. The –ve electrode is generally fixed and +ve
electrode is placed in adjustable holder and the
process is manual or automatic. The arc consists of
carbon vapors surrounded by orange red zone of
burning carbon and pale green flames.

Carbon Arc Lamp
When the lamp is OFF, the two electrodes are touching
each other due to spring pressure on +ve electrode.
When the supply is ON a large current is flow through
electrodes. The temperature of carbon electrode is
increased and thus the +ve electrode is pulled away
against its spring pressure through a small distance by coil
and thus an arc is struck between electrodes. This arc is
maintained by transfer of carbon particles from one
electrode to other electrode.

Carbon Arc Lamp
These particles travel from +ve electrode to –ve electrode,
thus after sometime of operation +ve electrode become
hollow and –ve become pointed. That’s why +ve
electrode is made double than –ve electrode.
In carbon arc lamp 85 % of light is given by +ve electrode
which produces high intensity light and only 10 % by –ve
electrode and 5 % by air. The temperature of +ve
electrode is 4000 oC and that of –ve electrode is about
2500 oC. The luminous efficiency of such lamps is about 9
lumen/watt.

ARC Lamps
For maintaining the arc, a minimum voltage required is
given by : V = (39 + 28 L ), where L is length of arc in
centimeter.

Filament or Incandescent Lamp
Working Principle :
As we know when a room heater is switched On , it
gives out red light with heat at the working
temperature of 750 oC and at this temperature the
radiations are mostly in infrared regions. This working
principle is used to develop the filament lamp.

Filament or Incandescent Lamp
When an electric current is passed through a fine
metallic wire , it raises the temperature of wire.
At low temperature only heat is produced but at
higher temperature light radiations goes on
increasing.
As filament lamp consists of fine wire of high resistive
material placed in an evacuated glass bulb. This type
of lamps are operated at the temperature of 2500 oC .

Incandescent Lamps
• One of the oldest
electric lighting
technologies.
• Light is produced by
passing a current
through a tungsten
filament.
• Least efficient – (4 to 24
lumens/watt).
• Lamp life ~ 1,000 hours.

Filament Lamp
A tungsten filament is enclosed in evacuated glass bulb but to
improve its performance some chemical like argon or nitrogen gas
are filled.

Properties of Metal for Filament
1. High melting point : so that it can be operated at high
temperature.
2. High specific resistance : so that it produces more heat.
3. Low temperature coefficient : so that filament
resistance may not change at operating temperature.
4. Low vapor pressure ; so that it may not vaporize
5. High ductile : so that it may withstand mechanical
vibrations

Tugnsten-Halogen Lamps
• A type of incandescent lamp.
• Encloses the tungsten
filament in a quartz capsule
filled with halogen gas.
• Halogen gas combines with
the vaporized tungsten and
redeposits it on the filament.
• More efficient.
• Lasts longer (up to 6,000
hrs.)

Sodium Vapor Lamp
This lamp consists of discharge tube made from special
heat resistance glass, containing a small amount of
metallic sodium, neon gas and two electrodes.
Neon gas is added to start the discharge and to develop
enough heat to vaporised sodium.
A long tube is required to get more light. To reduce
overall dimensions of the lamp, the tube is generally
bent into U-shape .

Sodium Vapor Lamp
Working Principle :
An electric discharge lamps require a high voltage at
staring and low voltage during operation.
So at starting a voltage of 450 V is applied across the
lamp to start the discharge. After 10 to 15 minutes, the
voltage falls to 150 V because of low power factor. To
improve the power factor a capacitor is connected
across the supply. The color of light produce is
yellowish.

A sodium-vapor lamp is a gas-discharge lamp that uses sodium in an
excited state to produce light.
There are two varieties of such lamps: low pressure and high pressure.
Low-pressure sodium lamps are highly efficient electrical light sources,
but their yellow light restricts applications to outdoor lighting such as street
lamps.
High-pressure sodium lamps have a broader spectrum of light than the
low pressure, but still poorer color rendering than other types of lamps.
Low-pressure and so inhibit sodium lamps only give monochromatic yellow
light color vision at night.

Mercury Vapor Lamp
On the basis of pressure inside the discharge tube, the
mercury vapor lamps are classified as high pressure
Mercury Vapor Lamp and low pressure Mercury Vapor
Lamp. High pressure M.V. Lamps are of following types :
1. M.A. type : these are operated at 220 -250 V A.C. main
and made in 250 W and 400 W.
2. M.A.T. type : these are made in 300 and 500 W and
operated at 200 -250 V A.C. as well as D.C.
3. M.B. type : This is operated at 200 – 250 V A.C. and
made in 80 W and 125 W.

Mercury Vapor Lamp
Construction :
It consists of hard glass tube enclosed in outer bulb of
ordinary glass. The space between two bulbs are
completely evacuated to prevent heat loss by convection
from inner bulb. The outer bulb absorbs harmful ultra
violet rays. The inner bulb contains argon gas with certain
quantity of mercury. In addition with two electrodes on
starting electrode having high resistance in series also
provided. The main electrodes are made of tungsten wire
in helical shape. The lamp has screwed cap and
connected to supply with choke. A capacitor is connected
across supply to improve power factor.

Mercury Vapor Lamp
Working Principle :
When the supply is switched ON, full voltage is applied
across main and starting electrodes. This voltage breaks
down the gap and discharge through argon gas takes
place. As the lamp warms up, mercury is vaporized , which
increase the vapor pressure. This discharge takes the
shape of intense arc. After 5 minutes, the lamp gives full
light.
It gives greenish blue color light .
this lamp is always suspended vertically, other wise inner
glass tube may break due to excessive heat.

The mercury vapor lamp is a high intensity discharge lamp. It uses an arc through
vaporized mercury in a high pressure tube to create very bright light directly from it's
own arc. This is different from fluorescents which use the mercury vapor arc to create
a weaker light that mainly creates UV light to excite the phosphors. The "Merc" as it is
known has been a workhorse for society; lighting streets, factories and large areas for
over 100 years.
Advantages
- Good efficiency (lamps after 1980s have a high lumen per watt rating)
- Color rendering is better than that of high pressure sodium street lights
- Some lamps last far longer than the 24000 hour mark, sometimes 40 years
Disadvantages
- Like many lamps it contains traces of mercury which must be disposed of properly
- HPS streetlights have a better lumen per watt rating
- Human skin looks green under the light, it is poor for color film/photography
-Warm up time required to start the lamp

Common uses: large areas like
parks, street lighting, high
ceiling buildings, gyms. Low
pressure lamps with a quartz
envelope are used for
germicidal purposes since they
allow UV light to pass.

High-pressure sodium lamps produce light from the yellow, red and orange
spectrums. Mercury vapor lamps produce light from the blue and green spectrums.
Neither lamp is necessarily good for the environment because of their mercury
content.
High pressure sodium lamps put out more lumens than mercury vapor lamps while
lasting about the same amount of hours before they need to be replaced.
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 vapor discharge lamp. With Sodium vapor
lamps a pre-heating heater is provided. The lamp glows initially with red color (Neon -
vapor discharge which is used as initiating gas) & then turns to orange yellow arc
(Sodium vapor discharge)
Light produced by high intensity discharge lamps can affect health in some instances.
Light in the blue spectrum can slow melatonin production and affect hormone levels.

Fluorescent Tube
it is a low pressure mercury vapor lamp. It consists
of a glass tube 25 mm in diameter and 0.6 m, 1.2 m
and 1.5 m in length. The tube contains argon gas at
low pressure about 2.5 mm of mercury. At the two
ends, two electrodes coated with some electron
emissive material are placed.

Fluorescent Tube
The colors produce by this tubes are as :
Material Color
Zinc silicate Green
Calcium tungsten Blue
Cadmium borate Pink
Calcium Holo phosphate White or day light
Magnesium tungsten Bluish white

Schematic of Fluorescent Lamp
Phosphor crystals Mercury atom Electron Electrode

Fluorescent Tube
Working :
A choke is connected in series with the tube which
act as a blast and provide a high voltage at starting
glow in the tube.
During running condition the same choke absorbs
some supply voltage and remain a voltage of 110 V
across the tube. A capacitor is connected to improve
the power factor.

Advantages of Fluorescent Tube
1. Voltage fluctuation has very small effect on light
output.
2. The luminous efficiency is more as length of rod is
more.
3. It gives light close to natural light.
4. Heat radiations are negligible.

Disadvantages of Fluorescent
Tube
1. Its brightness is less.
2. Initial cost is more
3. Overall maintenance cost is high.

Neon Lamp
These lamps are operated at a very low temperature of
about 200 oC that’s why these are called cold cathode
discharge lamps.
Two electrodes are housed at the two ends of the tube
which contain neon gas. The electrodes are made of iron
or nickel cylinder without any coating and practically they
do not emit electrons. It gives red light whereas with
mixture of mercury and argon it gives bluish green color.
Voltage require for starting and operation is 10000 V. This
high voltage is obtained from transformer.

Neon Lamp
Working :
When the supply is switched ON at primary side of
transformer, a voltage of 10000 V develops across
secondary side which come across two electrodes. At this
voltage a discharge occurs in neon gas.
Different colors can be obtained by changing the
constituents of gases and mercury filled in the tubes.

Neon Lamp
Applications :
Neon lamps are generally used for advertising. Most
of letters having two ends at which electrodes are
placed. In letter having more than two ends , the
tube path is repeated for some portion.

Halogen Lamp
Halogen lamp is a special type of tungsten filament
lamp which was developed in 1959, in this lams, a
small amount of halogen vapor is added to the inert
gas of the bulb. Its glass bulb is small in size and
mechanically strong. It operates at high temperature
of 3000 oC .

Halogen Lamp
When the supply is given to the lamp, a filament glows
and produce light. The halogen in addition to inert gas
causes the evaporated tungsten to resettle back on
the filament during cooling, that’s why lamp can be
operated at high temperature. It provides high
intensity light.

Advantages of Halogen Lamp
1. It is smaller in size.
2. It does not need any blast.
3. Good colors can be obtained.
4. Excellent optical control.
5. Gives same output throughout life
6. It has long life

Disadvantages of Halogen Lamp
1. During maintenance the handling of lamp is
difficult.
2. Radiant heat is more which heats the
surroundings.
3. Operating temperature is high which effects its
life.

Compact fluorescent Lamp( CFL)
The compact fluorescent lamps are becoming more and
more popular now a days because of their low
power consumption, low running cost, longer life,
attractive look, smooth light and low maintenance.
These lamps are available in different sizes and
designs. They have single rod, double rod, triple rod
or spiral rod. These lamps are available in different
power rating e.g. 5, 7, 9, 11, 18 and 24 watt 220 V

Compact fluorescent Lamp( CFL)
It is basically a low pressure mercury vapor
lamp having two electrodes coated with
electron emissive material placed in a
glass tube. The tube is coated internally
with some fluorescent material in the
form of powder. In the tube one drop of
mercury and argon gas is filled at low
pressure.

Compact Fluorescent Lamps (CFLs)
• Fluorescent lamp that is
small in size (~2 in. diameter,
3 to 5 in. in length).
• Developed as replacement
for incandescent lamps.
• Two Main Types
• Ballast-integrated.
• Ballast non-integrated (allows
only lamp to be replaced).

Compact Fluorescent
•Excellent color available – comparable to incandescent
•Many choices (sizes, shapes, wattages, output, etc.)
•Wide Range of CRI and Color Temperatures
•Energy Efficient (3.5 to 4 times incandescent)
•Long Life (generally 10,000 hours –
lasts 12 times longer than standard 750 hour incandescent lamps)
•Less expensive dimming now available (0-10v dimming to 5%)
•Available for outdoor use with amalgam technology

Compact Fluorescent Lamps (CFL) are compact, efficient, energy
saving,
having higher lifetime with reasonably good CRI & near daylight
illumination characteristics. Moreover they have all the accessories
inbuilt.
Hence they are better than traditional fluorescent lamps in terms of
economy and efficiency.

Compact Fluorescent Lamps (cont’d)
• Use ¼ the power of an
incandescent for an
equivalent amount of
light. (an 18-watt CFL is
equivalent to a 75-watt
incandescent.)
• 10,000 hour life. (10x
an incandescent).
• Saves about $30 over
the life of the CFL.

Ballasts
• Auxiliary component that
performs 3 functions:
• Provides higher starting
voltage.
• Provides operating voltage.
• Limits operating current.
• Old type ballasts were
electromagnetic.
• New ballasts are electronic.
• Lighter, less noisy, no lamp
flicker, dimming capability).

Ballast Factor
•DEFINITION: The fraction of rated lamp lumens produced by a specific lamp-
ballast combination
•APPLICATIONS: High Ballast Factor Increases output
(1.00-1.30) AND energy consumption
Typical Ballast Factor Comparable light output in
(0.85-0.95) one-to-one replacement
Low Ballast Factor Decreases light output
(0.47-0.83) AND energy consumption
•For optimal efficiency lamps and ballasts must be properly matched.
•Maximize energy savings by selecting electronic ballasts with ballast factor
that provides target illuminance.

Advantage of CFL
1. Low energy consumption.
2. Low maintenance cost
3. It stars instantly
4. It does not heat the surroundings
5. Excellent color properties
6. Low operating cost
7. More life

Applications of CFL
The compact size, longer life, low running
and maintenance cost, instant glow
makes these lamps suitable for all
places where uniform illumination is
required.
It is used in offices, shops, hotels,
hospitals, cinema halls, residential
buildings etc.

Measurement of Candle Power
The candle power of a source in any
given direction is measured by
comparing it with a standard or
substandard source with the help of an
optical instrument called
PHOTOMETER.

Photometer
Photometers are mostly based on inverse square law of
illumination and may be classified as stationary and portable
photometers.
The stationary photometers are usually installed in a dark room
with dead black walls and ceiling in order to eliminate error due
to reflected light.
Theportable photometers are direct reading instruments used to
measured illumination in houses, offices , commercial and
industrial places.

Rousseau‘s Construction
Only half of the vertical polar curve is shown in the figure below, since it is
symmetrical about the vertical axis. With O is the centre and radius OR
equal to the maximum radius of the polar curve, a semi-circle LRM is
drawn. A convenient number of points on this semi-circle (say 10° points)
are projected onto any vertical plane as shown. For example, points a,b,c
etc. are projected to d,e,f and so on. From point d, the horizontal line dg is
drawn equal to the intercept OA of the polar diagram on the radius oa.
Similarly, eh = OB, fk = OC and so on. The points g, h, k etc., define the
Rousseau figure. The average width w of this figure represents the
M.S.C.P. to the same scale as that of the candle powers in the polar curve.
The average width is obtained by dividing the Rousseau area by the base
of the Rousseau figure i.e. length lm which is the projection of the semi-
circle LM on the vertical axis. The area may be determined by Simpson‘s
rule or by using a planimeter

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

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.

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.

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.

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.

General Lighting
This system employs such type of luminaries, shades and
reflectors which give equal illumination in all the
directions.

Design of Indoor Light Scheme
While designing a good lighting schemes, the following
points must be kept in mind :
1. It should provide adequate illumination.
2. It should provides uniformly distributed light all over
working plane.
3. It should avoid glare and shadows as far as possible.
4. It should provide light of suitable colors.

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

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.

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

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.

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.

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.

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.

High Intensity Discharge (HID) Lamps

High Intensity Discharge Fixtures

High Intensity Discharge (HID) Lamps
• produces light by means
of an electric arc
between tungsten
electrodes housed inside
a translucent or
transparent fused quartz
or fused alumina
(ceramic) arc tube filled
with special gases.

High Intensity Discharge Lamps
(cont’d)
• Arc tube can be filled by various types of gases and
metal salts.
• HID lamps are used in industrial high bay
applications, gymnasiums, outdoor lighting, parking
decks, street lights.
• Efficient (up to 150 lumens/watt).
• Long Life (up to 25,000 hours).
• Drawback – take up to 15 minutes to come up to
full light after power outage.

High Intensity Discharge Lamps (cont’d)
• Types of HIDs
• Mercury Vapor
(obsolete)
• Sodium Vapor
• High pressure
• Low pressure
• Metal Halide
• Arc tube contains argon,
mercury, and metal
halides.
• Gives better color
temperature and CRI.

Metal Halide Lamps
• Most common HID in use today.
• Recent Improvements.
• Allow higher pressure & temperature.
• Better efficiency, better CRI and better lumen
maintenance.
• Pulse Start vs. older Probe Start
• Ceramic vs. older Quartz arc tube.

Light Emitting Diodes (LED)
• Latest Lighting Technology.
• Invented in 1962.
• In the past, used as indicator lights, automotive
lights, and traffic lights; now being introduced for
indoor and outdoor lighting.
• LED is a semiconductor technology.
• Electroluminescence. Electrons recombine with
holes in the semiconductor, releasing photons.

Light Emitting Diodes (cont’d)
• Lower energy
consumption.
• Longer lifetime (50,000
to 100,000 hrs).
• Smaller size.
• Faster switching.
• Greater durability and
reliability.
• Cycling.
• Dimming.

LED Replacement Lamps for a 4-ft.
Fluorescent Fxture

Comparison of LED with a Fluorescent
Lamp
EverLED-TR
Popular T8 Brand
Fluorescent
Watt Rating, typical B.F. = 0.8 22W 34W
Lumens, initial Equivalent 2850
CRI 85 85
Color Temperature 5000K 5000K
Life Expectancy 12 hrs per
start / 3 hrs per start
10 years 10
years
20000 hours 16000
hours
Light output at 0° C 20% increase 50% decrease

LED Applications
Successfully used today for many markets
• Signs & Traffic signals (most common)
• Displays (change colors for attention)
• Exit Signs (most common)
• Indicators and Flashlights
• Under Counter & Coves
• Accent
• Parking Garage & Outdoor
• Downlights
• Food Freezers

113
Comparison: LED to Ceramic Metal Halide
Cree LED Lighting LRP38 – Total Wattage = 36W
Ceramic Metal Halide – Total Wattage ~ 158 to 237W

Outdoor Lighting
• Older technology for
outdoor lighting
• High pressure sodium
• Metal Halide
• Newer technology
• Compact fluorescents
• LEDs
• Solar street lights
(economical when electric
lines don’t need to be run
in a new installation).

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