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
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.
Floodlighting

 It means ‘flooding’ of large surfaces with the help of

light from powerful projectors. Flooding is employed
for the following purposes :
 For aesthetic purposes as for enhancing the beauty of
a building by night i.e. flood lighting of ancient
monuments, religious buildings on important festive
occassions etc.
 For advertising purposes i.e. flood lighting, huge
hoardings and commercial buildings.
 For industrial and commercial purposes as in the case
of railway yards, sports stadiums and quarries etc.
FLOODLIGHTING
 Usually, floodlight projectors having suitable
reflectors fitted with standard 250-, 500-, or
1,000-watt gas-filled tungsten lamps, are
employed.
SOURCES OF ILLUMINATION
 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 aday
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
manually 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 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
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 C and that of –ve
electrode is about 2500 C. The luminous efficiency of
such lamps is about 9 lumen/watt or 12 lumen/watt
FILAMENT OR INCANDESCENT LAMP
 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 LAMP
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
Incandescent Lamp Characteristics
SODIUM VAPOR LAMP
 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.
SODIUM VAPOR LAMP
MERCURY VAPOR LAMP
 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.
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
FLUORESCENT TUBE
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 of110 V across the tube.
 A capacitor is connected to improve the power
factor.
FLUORESCENT TUBE
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 lamps, 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
PHOTOMETER
 Photometers are mostly based on inverse square
law of illumination and may be classified as
stationary and portable photometers.
 The portable photometers are direct reading

instruments used to measured illumination in

houses, offices , commercial and industrial
places.