Chapter 2 Lighting SOURCE ALONG WIYH LAMP

CHAPTER TWO
LIGHTING SOURCES AND THEIR
APPLICATIONS
2.1. Introduction
2.2. Artificial light sources and their applications
1

2.1. Introduction
Light is a form of energy, which is radiated or sent out from a
source in a waveform.
Light sources:
Natural light sources: occur within nature and are beyond the
control of people.
Man-made light sources: can be controlled by people, more
or less when and in the amount wanted.
2

• Natural light sources:
Sunlight
Moonlight
Starlight
Various plant and animal sources
3
Natural Lighting sources

2.2. Artificial light sources and their applications
• Man-made (artificial) lighting sources:
Wood flame
Oil flame
Gas flame
Electric lamps
Photochemical reactions
Various reactions such as explosives
4

Cont.
• The goal of artificial lighting is to create a visual environment that best
fulfills the functions intended, such as work, recreation, or rest.
• A good visual environment allows us to focus on the information of
interest, without the destruction of competing non-relevant information
called visional noise.
5

Cont.
• Visual noise can be excessive brightness or glare, background of
dominant pattern, reflections competing with the image, etc.
• There are different artificial lighting sources with different efficiency
and lighting quality.
• Artificial lighting sources with natural light quality in color rendition
and color appearance are generally expensive.
6

Cont.
• Electrical lighting design has to be coordinated with daylight or natural
lighting in such a way that the electrical light is switched off when the
natural light gives sufficient illumination or
• Deemed the artificial lighting automatically to keep the combined
natural and artificial lighting illumination level at a required level.
7

Cont.
• The electrical lighting is mainly used for decorative purpose, advertising, traffic
control, medical field and street lighting etc.
• Electrical lighting has the following advantages:
• Cleanliness
• Easy to control/handle
• Economical
• Steady output
• Better reliability
• Suitable for almost all purposes etc.
8

Cont.
1.2.1. Characteristics of light sources
Characteristics of electric light sources include:
a. Efficiency
• The efficiency of a lamp refers to the number of lumens leaving the lamp
compared to the number of watts required by the lamp (and ballast).
• It is expressed in lumens/watt.
• Sources with higher efficiency require less electrical energy to light a space.
9

Cont’d
b. Color Temperature
•This is a measurement of “warmth” or “coolness” provided by the lamp.
•People usually prefer a warmer source in lower illuminance areas, such as dining
areas and living rooms, and a cooler source in higher illuminance areas.
•Color temperature refers to the color of a blackbody radiator at a given absolute
temperature, expressed in Kelvins.
•A “warm” color light source actually has a lower color temperature.
10

Cont.
• A blackbody radiator changes color as its temperature increases (first to red, then to
orange, yellow, white, and finally bluish white at the highest temperature).
• For example, a cool-white fluorescent lamp appears bluish in color with a color
temperature of around 4100 K.
• A warmer fluorescent lamp appears more yellowish with a color temperature around
3000 K.
11

c. Color Rendering Index
• The color-rendering index (CRI) scale is used to compare the effect of a light
source on the color appearance of its surroundings.
• A scale of 0 to 100 defines the CRI.
• A higher CRI means better color rendering, or less color shift or distortion.
• CRIs in the range:
75-100 are considered excellent
65-75 are good
55-65 is fair
0-55 is poor 12

Cont.
The different methods of producing light by electricity may, in a broad sense, be
divided into three groups.
• By passing an electric current through a filament (by temperature incandescence)
• By developing arc between two electrodes
• By electric discharge through vapors or gases
13

Cont..
In by passing an electric current through a filament an electric current is passing
through a filament of thin wire placed in vacuum or an inert gas.
The current generates enough heat to raise the temperature of the filament to
luminosity.
Incandescent tungsten filament lamps are examples of this type and since their output
depends on the temperature of their filaments, they are known as temperature
radiators.
14

Cont..
• An arc lamp is an electric light that produces light by an arc of electrical current
passing through ionized gas between two electrodes.
• The gas within the bulb often consists of argon, metal halide, mercury, neon, sodium,
or xenon.
• The fluorescent light is a commonly used arc lamp that is a type of mercury arc lamp
whose bulb has been coated with phosphor.
The electrical requirements of a lighting system depend to a considerable extent on
the kind of lamps used.
15

1.2.2. Types of Electrical light Sources
There are two types of electric
light sources depending on the
principle of energy conversion,
filament type and electric
discharge types.
• The filament types
• incandescent lamps
• tubular strip lights,
• oven lamps,
• infrared heating lamps,
• spot- and floodlights,
• tungsten-halogen lamps
• Electric discharge lamps
• mercury vapour lamps
• sodium vapour lamps
• halide lamps
• fluorescent lamps, etc.
16

1. The Filament Types
17
Filament lamps produce light by heating a filament until it glows.
It can further be divided as
• Incandescent lamps
• Halogen lamps
a) Incandescent or Tungsten filament lamps
• It consists of a glass globe and a fine wire known as filament within it.
• When an electric current is passing through a fine metallic wire, heat is produced and
the temperature of the wire increases.

Cont.
• At low temperature the wire radiates heat energy, as the temperature of the wire
increases due to heating it radiates heat as well as light energy.
• The higher the temperature of the wire, the amount of light energy radiated is very
high.
• Tungsten has a melting point of 3382°C, and most modern lamps have filaments
running at about 2800°C, although some special lamps may run at 3220°C.
• The color of the light produced depends on the temperature, becoming whiter as the
temperature rises.
18

Cont.
• At 2800°C, it is rather yellow, but as no material is known which can be operated at a
higher temperature than tungsten, lamps of this type cannot be made to give a daylight
color.
• To prevent the filament from oxidizing, all the air must be evacuated from the bulb,
and the early lamps were of the vacuum type.
19

Cont.
• There are other materials which can be used for the filament carbon, osmium and
tantalum. These materials have high melting point (3500℃), (3,045 °C), (2,996 °C),
respectively.
• There are two types of incandescent lamps:-
i. Vacuum filled lamps :- are lamps where air is evacuated from the glass bulb
just to prevent oxidation of the filament. They are evacuated b/c tungsten has
a property to react with the oxygen in the air and quickly evaporate.
20

Cont.
ii. Gas filled lamps:- the glass bulb is filled with inert gases, filling the bulb with an
inert gas slows bulb blackening, which is caused by condensation of evaporated
tungsten particles on the inner bulb wall.
• operates up to around 25000c.
• in this lamps, the bulb is so bright that it is given an opaque coating internally.
• Gas filled lamps have filaments either single coiled or coiled coil.
21

22
Fig. 1.5 Basic components of Incandescent /tungsten lamps.

Cont.
A. Bulb: Soft glass is generally used. Hard glass is used for some lamps to withstand
higher bulb temperatures and for added protection against bulb breakage due to
moisture. Bulbs are made in various shapes and finishes.
B. Filament: The filament material is generally tungsten. The filament may be a
straight wire, a coil or a coiled-coil.
C. Lead-In Wires: Made of copper from base to stem press and nickel-plated copper
or nickel from stem press to filament, they carry the current to the filament.
D. Tie Wires: Molybdenum wires support lead-in wires.
23

Cont.
E. Stem Press: The lead-in wires in the glass have an airtight seal here and are made
of a nickel-iron alloy core and a copper sleeve (Dumet wire) to assure about the
same coefficient of expansion as the glass.
F. Exhaust Tubes: Air is exhausted out of and inert gases are introduced into the
bulb through this tube during manufacturing. The tube, which originally projects
beyond the bulb, is then sealed off short enough to be capped by the base.
G. Base: This is where electrical contact is made. One lead-in wire is soldered to the
center contact and the other soldered or welded to the upper rim of the base shell.
Made of brass or aluminum.
24

Cont.
H. Gas: A mixture of nitrogen and argon is used in most lamps 40 watts and over. Gas
slows down the evaporation of the filament.
I. Support Wires: Molybdenum wires support the filament.
J. Button: Glass is heated during manufacturing & support and tie wires placed in it.
K. Button Rod: Glass rod supports the button.
L. Heat Deflector: Used in higher wattage general service lamps and other types
when needed to reduce circulation of hot gasses into neck of bulb.
M. Fuse: Protects the lamp and circuit by blowing if the filament arcs
25

Cont.
26
Fig 1. Filament arrangments a) Sigle coil b) Coiled Coil

• The light output of incandescent lamps is about 10 to 15 lm/W.
• The efficiency of a tungsten lamp will depend on several factors, including the age of the
lamp and its size.
• This type of lamp is used only in situations that do not require a high level of illumination.
• The average lifetime of incandescent lamps is about 2000hrs when operating at rated
voltage.
• Incandescent lamps suffer from two disadvantages;
- Low efficiency and
- Colored light.
27
Cont.

Cont.
• The luminous efficacy varies between 8lum/W and 22lum/W.
• Incandescent lamps are sensitive to voltage variations.
• For incandescent lamp of a particular voltage rating, if a voltage lower than the rated
voltage is fed to the lamp, it will result in a dim light. The light will also be more
yellow in color, and the lamp might last a little longer.
• On the other hand, if the lamp is fed with a voltage slightly higher than the rating, the
light will be brighter, whiter, and the lamp will not last as long as it should. If the
voltage is significantly larger than the rating, it may burnout in one brief flash of light.
28

Cont.
29
 The following is empirical formula relating the luminous output of a lamp
and the applied voltage.
ɸ = ɸ0
𝑉
𝑉
𝑜
3.38
 Where ɸ is the incandescent lamp luminous flux output at voltage
V and ϕo is luminous flux output at voltage V0.
 The lamp wattage indicates the amount of power consumed by the lamp. Lamps
with higher wattage usually burn brighter. 100-Watt lamp will burn brighter than a
50-Watt lamp. However, the output may not be linearly related to the wattage.

Cont.
• A common incandescent lamp broadcasts light in all directions (have spherical light
pattern). Some lamps have built-in reflectors and/or lenses that let them throw a beam
with predictable characteristics.
Table: 1-2 typical incandescent lamps Efficiency increase as wattage increase
30
Power rating(Watts) 15 25 40 60 100 150 200 300 500 1000
Efficiency (Lum/w) 8 9 9 10 12 14 15 16 17 19

b. Halogen Lamps
• Another type of filament lamps is the halogen lamp. A halogen lamp also uses a
tungsten filament encased inside a much smaller quartz envelope.
• The quartz envelope is so close to the filament & the filament becomes about 4 times
hotter than a standard incandescent lamp resulting in more light per unit of energy.
• Gas filled inside the envelope is from the halogen group, commonly used is either
iodine or bromine or sometimes mixture of both.
• The halogen gas will combine with tungsten atoms as they evaporate and redeposit
them on the filament wire instead of being deposited on the glass and darkening it.
31

Cont.
• In a conventional incandescent lamp, the filament loses material by evaporation.
• The inert gas inside the bulb reduces the rate of evaporation but cannot prevent it completely.
• A further improvement can be obtained by adding a halogen to the gas, which gives rise to a
reversible chemical reaction.
• Tungsten evaporates from the filament and diffuses towards the bulb wall.
• Provided the temperature is favorable, the tungsten combines with halogen at the walls and the
resulting tungsten halide diffuses back to the filament.
• As the temperature prevailing at the filament, the tungsten halide dissociates into tungsten and
halogen and the tungsten is deposited back on the filament.
32

Cont.
• Successful operation of halogen lamp depends on the achievement of suitable
temperatures at both the filament and the bulb wall.
• This makes it necessary for the filament to be at a higher temperature than in an
ordinary tungsten lamp and for the bulb to be smaller.
• The bulb has to be at a temperature of about 250°C, and in order to withstand this it
has to be made of fused silica or high melting-point glass.
• For a given power, a tungsten halogen lamp has a longer life and a higher light output
than an ordinary tungsten lamp.
33

Cont.
 The high temperature makes it of limited use in domestic or commercial lighting but
it finds application in floodlighting and the lighting of film and television studios.
 The inside of the bulb remains free of deposits and clean through the lamp life. The
technique increases the efficiency of the halogen lamps 12 to 24 lumens/Watt. The
life of such lamps also extends 2000 to 4000 hours’.
34

Cont.
As a result of high temperature, halogen lamps produce ultraviolet (UV) and infrared
(IR) energies than conventional incandescent lamps. Bulb coatings are usually used to
filter the UV and reflect the IR back on to the filament improving the efficiency.
Halogen lamps have a CRI of 100.
35
Fig. 1.7. Typical halogen lamp

2. Discharge lighting
• This type of lighting relies on the ionization of a gas to produce light.
• Light from discharge lamps is not produced by heating a filament, but by exciting
gases or metal vapors.
• This is done by applying voltage b/n two electrodes located in a discharge tube filled
with inert gases or metal vapors. Then, current is produced b/n the two electrodes.
• On their way through the discharge tube, the electrons collide with gas atoms, which
are in turn excited to radiate light, when the electrons are travelling at a sufficiently
high speed.
36

Cont.
• In all discharge lamps, an electric current is passing through a gas or vapour which
renders it luminous.
• The color and intensity of light (candle-power) produced depends on the nature of the
gas or vapour only.
• For every type of gas, there is a certain wavelength combination; radiation, i.e. light,
is produced from one or several narrow frequency ranges.
 The elements most commonly used in this process of producing light by gaseous
conduction are neon/Decorative neon sign, mercury and sodium vapour.
37

Cont.
 Discharge lamps are of two types.
The first type consists of those lamps in which the color of light is the same as
produced by the discharge through the gas or vapour. To this group belong the
neon gas lamps, mercury vapour and sodium vapour lamps.
The other type consists of vapour lamps which use the phenomenon of
fluorescence.
38

Cont.
• The wavelength of the radiation depends upon the gas, its pressure and the metal
vapor used in the lamp.
• The colour of the light emitted depends upon the type of gas used. The colour
obtained from some of the gases & vapours commonly employed are listed in the
table below.
39

a. Sodium Vapour Lamps
They have a starting time of 5 to 6 minutes. They go off and cannot be restarted after
the recovery of the voltage till its value falls to the normal value.
The color of their light is yellowish and produces color distortion. Their initial cost of
installation is maximum although their running cost is less than for filament lamps but
more than for fluorescent lamps.
Change in voltage affects their starting time and color of their radiations.
They work on ac voltage and frequent switching affects their life.
Not suitable for residential lighting.
40

Cont.
a. b.
Fig: a. low-pressure sodium- vapour lamp and b. high-pressure sodium-
vapour lamp
41

Low-pressure sodium- vapour lamp
• It consists of a U-shaped double-thickness glass tube. The inner wall of which is low-
silica glass which can withstand attack by hot sodium.
• Inside the tube there is a quantity of solid sodium and a small amount of neon gas
(this helps to start the discharge process).
• The light output is almost pure yellow, which distorts surrounding colors, and as such
is useful only for street lighting.
Fig. circuit connection of low-pressure sodium- vapour lamp
42

Cont.
 The lamp is surrounded by an outer glass envelope B which serves to reduce the loss
of heat from the inner discharge tube A.
 In this way, B helps to maintain the necessary high temperature needed for the
operation of a sodium vapour lamp irrespective of draughts.
 The capacitor C is meant for improving the power factor of the circuit.
43

Cont.
 It requires a high voltage at staring and low voltage during operation. So at starting a
voltage of 450V is applied across the lamp to start the discharge. The discharge is first
started in the neon gas (which gives out reddish color).
 After 10 to 15 minutes, the voltage falls to 150V because of low power factor.
 After a few minutes, the heat of discharge through the neon gas becomes sufficient to
vaporize sodium and then discharge passes through the sodium vapour.
 In this way, the lamp starts its normal operation emitting its characteristic yellow light
44

Cont.
 The tungsten-coated electrodes are connected across auto-transformer T having a
relatively high leakage reactance.
 The leakage reactance is used not only for starting the current but also for limiting its
value to safe limit.
 The electric discharge or arc strikes immediately after the supply is switched on
whether the lamp is hot or cold.
 The normal lighting position of the lamp is horizontal although two smaller sizes of
lamp may be lighting vertically.
45

Cont.
Advantage
Long life
Good lumen maintenance through
out its life
Reliable cold weather starting
Prompt reigniting after a temporary
power interruption
Disadvantage
Produce sever color distortion
Relatively long warm-up time
Application
Used mainly for outdoor lighting
application such as lighting streets/road
ways, railways, and flood lighting.
Reading assignment High pressure
sodium Vapour lamps 46

b. Mercury Vapour Lamps.
 They take 5 to 7 minutes for starting.
 They go off and cannot be restarted after the recovery of the voltage till the pressure
falls to normal and suffer from high color distortion.
 Their initial cost of installation is high but lesser than that of fluorescent lamps. Their
running cost is much less than incandescent lamps but higher than fluorescent tubes
for the same levels of illumination.
 Mercury-vapour light is always bluish green and deficient in red rays.
47

Cont.
 They are suitable for open space like yards,
parks and highway lighting etc. Change in
voltage affects their starting time and color of
radiations emitted by them.
 Switching does not affect their life period.
 They are suitable for vertical position of
working.
 They have an average working life of 3000 hrs
and an efficiency of 40 lm/W.
48
Figure: Mercury Vapour Lamps

High pressure mercury vapour lamps
• It consists of a quartz tube containing mercury at high pressure and a little argon
gas to assist starting. There are two main electrodes and auxiliary electrode.
• As shown in Figure below, the main electrodes are D and E whereas S is the
auxiliary starting electrode. S is connected through a high resistance R (about 50
kΩ ) to the main electrode situated at the outer end of the tube.
 The main electrodes consist of tungsten coils with electron-emitting coating or
elements of thorium metal.
49
Fig. Basic Circuit of High pressure mercury vapour lamps

Cont.
 A choke is provided to limit a current to a safe value.
• A capacitor is connected in parallel to the lamp to improve its power factor.
• The initial discharge takes place in the argon gas between the auxiliary (starting)
electrode and main electrode close to it.
• This causes the main electrode to heat up and the main discharge between the
main electrodes takes place.
50

Cont.
51
Fig. high-pressure mercury vapour lamps: (a) basic circuit (b) modern mercury vapour lamp.

Low-pressure mercury-vapour lamp (Fluorescent)
• It is more popularly known as a fluorescent lamp, consists of a glass tube, the interior
of which is coated in fluorescent phosphor.
• Certain materials, such as calcium phosphate, emit visible light whenever they absorb
ultra-violet light.
• The tube is filled with mercury vapour at low pressure and a little argon to assist
starting. At each end of the tube an oxide-coated filament is situated.
• Discharge takes place when a high voltage is applied across the ends of the tube.
52

Fluorescent lamp (Low pressure mercury vapour lamps):
 Fluorescent lamp is an electric lamp that produces light through fluorescence.
 In most fluorescent lamps, a mixture of argon and mercury gas contained in a glass
bulb is stimulated by an electric current, producing ultraviolet rays.
 These rays strike a fluorescent phosphor coating on the interior surface of the bulb,
causing it to emit visible light.
 Fluorescent lamps are much more efficient than incandescent lamps because very
little energy is lost as heat.
53

Cont.
• The inner wall of the tube is coated with fluorescent powder which
transforms Ultraviolet radiation in to visible radiation or light.
• The light output of a fluorescent lamp is 70 lm/w and has an average life of about
7500 hrs.
 The starter left open while the lamp is lighting; the electrodes maintain their
operating temperature as long as they continue to pass the discharge current.
54

Stroboscopic Effect
The disadvantage of fluorescent lamp is that, as the alternating discharge current
passes through zero twice every cycle, the light produced tend to flicker at twice
of main frequency.
Machinery rotating at a certain speed may appear to be stationary or moving
more slowly than it really is. This is known as the stroboscopic effect.
While a fluorescent lamp is in operation the light may flicker. Under some
circumstances this may make it appear that rotating machinery has slowed down
or even stopped.
Stroboscopic effect is an undesirable state of affairs which is usually remedied
by one of the two following methods.
55

Solution for Stroboscopic effect
• Balancing the lighting load (three phase)
If a large lighting load is installed in a three-phase installation where there is some
rotating machinery, the stroboscopic effect may be overcomed by connecting
alternate groups of lamps to a different phase.
 The lead–lag circuit
In this method a capacitor is wired in series with every alternate lamp in a group.
The value of the capacitor is such that the lamp unit it is fitted to has an overall
leading PF. This means that any pair of lamps have a lagging and a leading PF.
This has the effect of cancelling out the resultant flicker, in the same way as two
equal but opposing forces cancel each other out
56

Cont.
 Typical mercury-vapour lamp applications are :
 Industrial lighting:-where high level illumination is required and
color rendition is not important.
 Flood-lighting ,street-lighting and security lighting
 Photochemical applications :- where ultra-violet output is useful as
in chlorination, water sterilization and photocopying etc.
57

Individual Assignment (Max 10 points)
1. Compare CFL, Incandescent and LED Lamps?
2. Compare LED, Mercury vapour and high pressure Sodium Vapour in Street lights?
• Your paper should address atleast the following issues.
Brief description of each equipments (Definition and How they work )
Their advantage and disadvantage and application areas
Initial cost (Starting cost) and Running /operation cost
Regular service and maintenance
Life time of the equipments
• Submission Date December 17, 2024.
58

Chapter 2 Lighting SOURCE ALONG WIYH LAMP

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