Utilization of electrcal energy part 1 unit 1

1. Illumination
Dr. K. D. Patil
EE6I – Utilization of Electrical Energy (UEE-22626)

1. Introduction:
 Light is electromagnetic radiation within a certain portion of
the electromagnetic spectrum. The word usually refers
to visible light, which is visible to the human eye and is
responsible for the sense of sight.
 The electromagnetic spectrum spreads over a tremendous
range of frequencies or wavelengths. The wavelength (λ) is
related to the frequency (f): c=f λ, c is constant=3x108 m/sec
 Visible light have wavelengths that range from 0.00004 to
0.00007 cm or 400 to 700 nm or 4000 to 7000 Angstrom (A)
 Light of different wavelengths produces sensation of
different colours to human eye. e.g. 7000 A = Red, 6000 A=
Yellow, 4750 A = Blue, 4000 A Violet

2. Illumination Terminology:
(i) Light: Light is defined as the radiant energy from a hot body
causing visual sensation upon the human eye.
(ii) Luminous Flux: Luminous flux is defined as the total
quantity of light energy radiated or emitted per second from a
luminous body in the form of light waves.
Its unit is Lumens and it is denoted by F or ϕ
(iii) Luminous Efficiency or Radiant Efficiency: It is defined
as the output in Lumens per watt of the power consumed by the
source of light.
Its unit is Lumens per watt (Lumen/watt)
(iv) Plane Angle: Plane angle is subtended in a plane by two
converging lines.
Its unit is radians (rad) or degree (0) and it is denoted by (θ).

(v) Solid Angle: Solid angle is the angle generated by the line
passing through the point in space and the periphery of the area.
Its unit is Steradians and it is denoted by (ω).

(vii) Lumen: Lumen is defined as the amount of luminous flux
given out in space represented by one unit of solid angle by a
source having an intensity of one candle power in all directions.
Lumen = Candle Power x Solid Angle = C.P. x ω
Total Lumens given out by the source of one candela is
4π Lumens.

(x) Meter Candle: Meter Candle or Lux is defined as the
illumination produced by a source of one candle power placed
at the centre of the sphere on the inner surface of a sphere of
one meter radius.
(xii) Mean Horizontal Candle Power (M.H.C.P.): M.H.C.P. is
defined as the average value of the candle powers of a source of
light in all directions in horizontal plane passing through the
source.

(xiii) Mean Hemispherical Candle Power (M.H.S.C.P.):
M.H.C.P. is defined as the average value of the candle powers
of a source of light in all directions above or below the
horizontal plane passing through the source.

(xxii) Waste Light Factor:
This factor is taken into consideration in flood lighting. In flood
lighting light projectors (Focus) are used. So there is overlap of light from
two or more projectors also all the light does not fall on the object to be
illuminated. To compensate this light waste light factor is taken in flood
lighting.
The value of waste light factor is taken as 1.2 for regular
objects (Buildings) and 1.5 for irregular objects (statues)
(xxiii) Beam Factor: Beam factor is the ratio of lumens in the beam of a
projector to lamp lumens.
This factor takes into account the absorption of light by reflector
and front glass of the projector lamp.
The value of beam factor lies between 0.3 to 0.6.

(xxiv) Glare: Glare is a visual sensation caused by excessive and
uncontrolled brightness. It can be disabling or simply uncomfortable. It is
subjective, and sensitivity to glare can vary widely. Older people are
usually more sensitive to glare due to the aging characteristics of the eye.
(xxv) Point Source: Point source is the conceptual light source or lamp in
the form of point (i.e. zero dimensions).
In the study of illumination engineering, irrespective of shape and
size of the light sources or lamps, all the light sources or lamps are
considered as point sources.
(xxvi) Shadow: A shadow is a dark (real image) area where light from a
light source is blocked by an opaque object. It occupies all of the three-
dimensional volume behind an object with light in front of it.
A point source of light casts only a simple shadow, called an
"umbra". For a non-point or "extended" source of light, the shadow is
divided into the umbra, penumbra and antumbra. The wider the light
source, the more blurred the shadow becomes.

3. Laws of Illumination:
The illumination of a surface due to point sources is
governed by the following two laws of illumination.

Simple Numerical on Laws of Illumination:
Problem 1: The candle power of a lamp placed normal to a working
plane is 30 CP. Find the distance, if the illumination on the
working plane is 15 Lux.

Problem 2: When a 250 V lamp takes a current of 0.8 Amp, it
produces a total flux of 3260 Lumens. Calculate (i) MSCP
(ii) Lamp efficiency.

Problem 3: The luminous intensity of a lamp is 400 candela and is
placed in the middle of a 10m x 5m x 4m room. Calculate the
illumination, (i) in each corner of the room, (ii) the middle of 5m
wall.
θ
4m
10m
C
B
D
O
L
A

Problem 4: Calculate the total luminous flux from the lamp having
mean spherical candle power (M.S.C.P.) of 35.

Problem 5: A 250 volt lamp has a total flux of 3000 lumens and
takes a current of 0.8 Amp. Calculate (i) Lumens/watt, and (ii)
M.S.C.P./watt.

Problem 6: The illumination at a point on a working plane directly
below the lamp is to be 100 Lumens/m2. The lamp gives 256 C.P.
uniformly below the horizontal plane. Determine the height at
which the lamp is suspended and find illumination at a point on
the working table 1.2 m away from the vertical axis of the lamp.

4.1 Low Pressure Mercury Vapour Lamp OR
Fluorescent Tube:
Construction:

Working Principle:
 When switched on, full voltage comes across the tube through
the ballast and the fluorescent lamp starter. No discharge
happens initially. But when starter makes and breaks the circuit,
very high e.m.f. is induced in the choke.
 This high voltage comes across the tube electrodes and strikes
the mixture of argon gas and mercury vapour. Initially discharge
starts through argon gas and then through the mercury vapour.
 This current excites the mercury atoms, causing them to emit
non-visible ultraviolet (UV) radiation.
 This UV radiation is converted into visible light by the
phosphors lining the tube.
 Fluorescent lamp require a choke or ballast to provide correct
starting voltage and to regulate the operating current after the
lamp has started.

Advantages:
 Energy efficient- so far the best light for interior lighting
 Low production cost.
 Long life of tubes
 Can give desired colour light output from cool whites to warm whites.
 Gives diffused light.
Disadvantages:
 The flicker of the high frequency can be imitated to humans
 Due to flickers fluorescent lamp light produce stroboscopic effect.
 Ballasts can create radio interference.
 Toxic metal mercury is used.
Applications:
 Residential Lighting
 Commercial Lighting
 Street Lighting
 Industrial or Factory Lighting

4.2 CFL (Compact Fluorescent Lamp):
Construction:
There are two types of CFLs: integrated and non-
integrated lamps. Integrated lamps combine the tube and
ballast in a single unit. These lamps allow consumers to replace
incandescent lamps easily with CFLs.

Working Principle:
 CFL has two components: (i) A glass tube filled with argon and
mercury vapour and coated with a layer of fluorescent material, (ii) An
ballast electronic circuit.
 The ballast electronic circuit takes a 230 V, 50 Hz AC input from
external power source and sends a current into the fluorescent tube as
output. When power supply is given to the CFL, filament attached
with the cathode heats up and emits electrons in the tube. This ionizes
the argon and mercury vapour particles thus in CFL visible light is
produced by fluorescence.
 CFLs are up to four times more efficient than incandescent bulbs.
 While, initially, they cost more, CFLs are less expensive in the long
run because they last much longer than incandescent bulbs.
 CFLs are highly versatile and can be used in any setting that you
would normally use incandescent bulbs.
 As compared to incandescent bulbs CFLs produce much less heat.
Advantages:

Disadvantages:
 Frequent on and off operation of CFL can reduce their lifetime
substantially.
 Generally CFLs are not suitable for using with dimmers.
 CFLs are not suitable for focused or spotlights or where narrow beams
of light are required.
 CFLs are fragile and needs careful handling.
 In CFL Mercury vapour is used and Mercury is a toxic metal.
Applications:
CFLs are used for general purpose lighting. The various fields of
applications of CFLs are:

4.3 High Pressure Mercury Vapour (HPHV) Lamp:
4.1 Construction and Working:
The mercury vapour 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.

Advantages:
 Good efficiency
 Colour rendering is better than that of high pressure sodium
street lights.
 Long life.
Disadvantages:
 Contains traces of mercury which must be disposed of
properly.
 Warm up time required to start the lamp.
 Not suitable for colour film/photography.
Applications:
 Street Lighting

4.4 Sodium Vapour Lamp:
Construction and Working:
A sodium-vapour lamp is a gas-discharge lamp that
uses sodium in an excited state to produce light at a
characteristic wavelength near 589 nm.

Advantages:
 Good efficiency
 Near day light colour output.
 Long life.
Disadvantages:
 Expensive than mercury vapour lamp.
 Warm up time required to start the lamp.
 Not suitable for colour film/photography.
Applications:
 Flood lighting
 Street lighting
 Industrial or Factory lighting

4.5 Metal Halides Lamp:
Construction: Metal-halide lamps consist of an arc tube with
electrodes, an outer bulb, ballast and a base.
Inside the fused quartz arc tube, two tungsten electrodes
doped with thorium are sealed into each end and an AC voltage
is applied to them through molybdenum foil seals fused in
silica. It is the arc between the two electrodes where the light is
actually created. The ends of the arc tube are often externally
coated with white infrared–reflective zirconium
silicate or zirconium oxide to reflect heat back onto the
electrodes to keep them hot and thermionically emitting.
Metal-halide lamps are fitted with an outer glass bulb to
protect the inner components and prevent heat loss. Metal-
halide bulbs require electrical ballasts to limit the arc's current
for arc stabilization. Edison screw or double-ended metal base
is used.

Working Principle:
 Like other gas-discharge lamps, metal-halide lamps produce
light by ionizing a mixture of gasses and metal halide in
an electric arc.
 The particular mixture of metal halides influences
the temperature and hence the colour, and intensity of
light.
 When a 230 V, 50 Hz AC supply is applied to lamp, at
starting the argon gas in the lamp is ionized first, which
helps to maintain the arc across the two electrodes, ballast
stabilizes the arc. The heat generated by the arc then ionizes
the mercury and metal halides into a plasma, which
produces an increasingly-brighter harsh white light.

Advantages:
 High luminous efficiency
 High power factor
 Excellent for applications where high intensity light is required.
Disadvantages:
 More expensive
 Slightly larger in size
Metal Halide lamps are used in numerous applications, such as:
 General Lighting
 Stage Lighting
 Photography Studio
 Film/T.V. Studio
 Sports Lighting
Applications:

4.6 LED (Light Emitting Diode) Lamp:
Construction:

Working Principle:
 In LED lamps a P-N junction semiconductor diode called
light-emitting-diode or LED is used as a source of light.
 A P-N junction can convert absorbed light energy into a
proportional electric current. The same process is reversed
here (i.e. the P-N junction emits light when electrical
energy is applied to it). This phenomenon is generally
called electroluminescence, which can be defined as the
emission of light from a semiconductor under the influence
of an electric field.

Advantages:
 Long service life.
 Efficiency – LED lamps are currently the most energy-
efficient light sources.
 Resistance to impact and temperature.
 LED lamps, compared to traditional lighting, generate small
amounts of heat.
 LED lamps do not contain toxic materials such as mercury
and other metals dangerous for the environment, and are
100% recyclable.
 Now a days, using LED lamps it is possible to obtain
colorful lighting.

Disadvantages:
 LED lamps are more expensive than a traditional lamps.
 Quality of LED lighting is highly dependent on the ambient
operating temperature.
LED lamps are used for both general and special-
purpose lighting. Such as:
 Flood Lighting
 Decorative Lighting
 Street Lighting
Applications:

4.7 Selection of Lamp:
Following factors are to be considered while selecting a lamp
for particular application -
(i) Lamp efficiency or Luminous efficiency of lamp.
(ii) Initial and running cost of lamp.
(iii) Lamp life.
(iv) Colour rendition and glare.
(v) Amount of light control desired.
(vi) Size and shape of the lamp.
(vii) Operating hours.

5. Types Lighting Schemes:
(i) Direct lighting
(ii) Indirect lighting
(iii) Semi direct lighting
(iv) Semi indirect lighting
(v) General diffusing lighting

(i) Direct Lighting:
The light from the source falls directly on the object or
the surface to be illuminated. With the help of shades and
globes and reflectors of various types, most of the light is
directed in the lower hemisphere.
Direct lighting, though most efficient, is liable to cause
glare and hard shadows.

(ii) Indirect Lighting:
In this form of lighting, light does not reach the surface
directly from the source but indirectly by diffuse reflection.
One of the main characteristics of indirect lighting is that
it provides shadow less illumination, which is very useful for
drawing offices, composing rooms and in workshops.
However, many people find purely indirect lighting flat
and monotonous and even depressive.

(iii) Semi-direct Lighting:
This system utilizes luminaries which send most of the
light downwards directly on the working plane but a
considerable amount reaches the ceilings and walls also.
Such a system is best suited to rooms with high ceilings
where a high level of uniformly-distributed illumination is
desirable.

(iv) Semi-indirect Lighting:
In this system which is, in fact, a compromise between
the first two systems, the light is partly received by diffuse
reflection and partly direct from the source.
Such a system, therefore, eliminates the objections of
indirect lighting mentioned above.

(v) General Diffusing Lighting:
In this system, luminaries are employed which have
almost equal light distribution downwards and upwards.
This system combines the advantages and eliminates the
disadvantages of all above systems of lighting.

6. Domestic and Industrial Lamp Fittings/Fixtures:

7. Electronic Ballast:
An electronic ballast is a device which controls the starting voltage
and the operating currents of lighting devices.
It does this through the principle of electrical gas discharge. An electronic
ballast will convert power frequency to a very high frequency to initialize
the gas discharge process in Fluorescent Lamps – by controlling voltage
across the lamp and current through the lamp.
Working Principle of an Electronic Ballast:
Electronic ballast takes supply at 50 – 60 Hz. It first converts AC
voltage into DC voltage. After that, filtration of this DC voltage is done by
using capacitor configuration. Now filtered DC voltage is fed to the high-
frequency oscillation stage where oscillation is typically square wave and
frequency range are from 20 kHz to 80 kHz.
Hence output current is with very high frequency. A small amount
of inductance is provided to be associated with a high rate of change of
current on high frequency to generate high valued . Generally, more than
400 V is required to strike the gas discharge process in fluorescent tube
light. When the switch is ON, the initial voltage across the lamp becomes
1000 V around due to high valued, hence gas discharge takes place
instantaneously.

Once the discharge process is started, the voltage across the lamp is
decreased below 230V up to 125V and then this electronic ballast allows
limited current to flow through this lamp. This control of voltage and
current is done by the control unit of the electronic ballast. In running
condition of fluorescent lamp, electronic ballast acts as a dimmer to limit
current and voltage.
Basic Circuitry of an Electronic Ballast:

Advantages of Electronic Ballast as Compared to
Electromagnetic Ballast:
1. It operates in low supply voltage. It produces high frequency to give
very high output voltage initially to start up the discharge process.
2. It creates very low noise during operation.
3. It does not create any stroboscopic effect or RF interference.
4. As it works with very high frequency, it helps to start the lamp
operation instantaneously.
5. It does not require any starter that is used in electromagnetic ballast.
6. It never creates flickering.
7. No start up vibration occurs.
8. Its weight is very minimal.
9. Ballast loss is very less. Hence energy saving is possible.
10. It increases the life of the Lamp.
11. Due to operation at higher frequency, discharge process in fluorescent
lamp is at higher rate. Hence quality of light is increased.

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