CHAPTER 1

INTRODUCTION TO ILLUMINATION
1.1. LIGHTING
 Light is defined as the radiant energy from a hot body, which
produces the visual sensation upon the human eye. The sensation of
color is due to the difference in wavelength of the light radiations.
White light, such as given by the sun, is composed of different colour
each having different wavelengths. These are:
0.300 – 0.436 micrometer--------------------Violet
0.436 - 0.495 >> ---------------------Blue
0.495 - 0.566 >> ---------------------Green
0.566 - 0.589 >> ----------------------Yellow
0.589 - 0.627 >> ----------------------Orange
0.627 - 0.780 >> -----------------------Red
 In general, light is an electromagnetic radiation such as radio waves,
x-rays e.t.c. We can classify electromagnetic waves as visible and
invisible waves.
* Visible waves: daylight, radiations from candles and lamps.
* Invisible waves: x-rays, gamma rays, radio waves.
v = fλ (v is speed of light, f is frequency and, λ is wave length )
Angstrom unit (Ǻ): 1Ǻ=10-8 cm=10-10 m
λ of red light = 7500 Ǻ
λ of violet light = 4000 Ǻ
λ of blue light =5000 Ǻ
λ of yellow light =6500 Ǻ
 Those colours of white light having wave lengths of less than 0.3
micro meter belongs to the ultra violet range and those with wave
lengths greater than 0.8 micro meter belong to the infrared range. The
visible spectrum ranges is from 0.4 to 0.7 micrometers.
 Human eye is most sensitive to light having wavelengths of about
0.555 micrometer in the green portion of the spectrum.
 Maximum power of light is radiated when the wavelength is about 0.5
micrometer, which is approximately the wavelength at which the
human eye is most sensitive.
  Illumination refers to the provision of sufficient lighting either by
natural means. (e.g. sun light) or artificial light sources (e.g. electric
lamps).

Terms used in Illumination

1. Luminous Flux: It is the total quantity of light energy radiated/

produced from a luminous body in the form of light waves. It is
measured in lumens. It is represented by symbol φ.

2. Luminous Intensity (I): It is the amount of luminous flux emitted by

a source per unit solid angle. It is measured in candela or lumens per
steradian. i.e.

I =φ / ω,
Where the solid angle is measured in Steradians (ω).
1 Candela = 1 Lumen / steradian is the angle generated by the surface
passing through the light point in space and periphery of the area. It was
denoted by ω. Solid angle was given by the ratio of the area of the surface to
the square of the distance between the area and the point. i.e. A / r2 . Since
the surface of a sphere has an area equal to 4πr2;
∴ Total angle, ω=4πr 2/ r2 = 4π stradians
3. Illumination (intensity of illumination) (E) - it is the luminous flux
received by a surface per unit area of surface. Its unit depends upon the units
in which area is measured. It is measured in lumens per square meter or lux
or meter candle. Mathematically,
E=φ/A
4. Luminous efficacy (k): a measure of unit lumens per watt (lm/W). It can
be thought of as the ‘efficiency’ of the light source.
5. Luminance, L: The luminous intensity (I) per unit of the apparent area of
the source of light (or illuminated areas).
L = I/A [cd/m2]
6. Coefficient of utilization:
This is a factor showing the ratio of the lumens reaching on the working
plane to the total lumens generated by the source. It depends on the
dimension of the room to be illuminated, the reflectance of the walls,
ceilings, and floors, the lamp output of reflectors and diffusers used and the
position of the lamp.
7. Maintenance Factor: The light obtained from a light source may be
affected by variables due to dire, ageing of the lamp, e.t.c. The MF takes in
to account such effects.

Illumination Laws
▪ Inverse square law:
The illumination of a surface is inversely proportional to the distance
between source & surface provided that the distance between the surface &
the source is sufficiently large so that source can be regarded as a point
source. This is known as Inverse square Law.

Illuminance E(lux) = luminous intensity(cd) = I

d2 d2

Fig 1.1 illumination on surface

Example
A light source of 900 cd is situated 3 m above a working surface. (a)
Calculate the illuminance directly below the source. (b) What would be the
illuminance if the lamp were moved to a position 4 m from the surface?

Cosine rule
From Fig. 1.2 it will be seen that point X is further from the source than is
point Y. The illuminance at this point is therefore less. In fact the
illuminance at X depends on the cosine of the angle θ . Hence,

EX= I X cos3 θ
d2

Fig.1.2

Example : A 250 W sodium-vapour street lamp emits a light of 22 500 cd

and is situated 5 m above the road. Calculate the illuminance (a) directly
below the lamp and (b) at a horizontal distance along the road of 6 m .

1.2. LIGHT SOURCE AND APPLICATION

Light is a form of energy, which is radiated or sent out from a source in a
waveform. It is part of a whole family of electromagnetic wave. Light
sources can either be natural (sun) or artificial (e.g. electric lamps).
Generally, electric lamps can be classified in to:
a) Incandescent lamps
b) Discharge lamps.
When an electric current passes through a fine metallic wire, heat is
produced and the temperature of the wire increases. 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.
 Incandescent lamps
The incandescent lamp consists of a glass globe completely evacuated or gas
filled and a fine wire known as filament, which is heated to white heat by the
passage of electric current. The filament of modern lamps are normally
made of tungsten since this material has a very high melting point (3400 0 c)
and can be manufactured in the form of a suitably thin wire. The bulbs of
smaller lamps are evacuated to prevent oxidization of the filament. But, in
many lamps, an inert gas such as argon is introduced. This enables the
filament to operate at a higher temperature without undue deterioration due
to the evaporation, which tends to take place in a vacuum.
The materials, which can be used for the filament, are: carbon, osmium,
tantalum and tungsten. These metals are selected due to their high melting
points.
 The main advantages of incandescent lamp are:
a) The filament has a more compact formation.
b) Heat losses due to convection currents in the gas are reduced, thus giving
a higher efficiency.
 There are two types of incandescent lamps:
1. Vacuum lamps
- air is evacuated from the glass bulb.
- operates only up to around 20000c.
2. Gas-filled
- the glass bulb is filled with inert gases(Ne or Ar)
- operates up to around 25000c.
- in gas-filled lamps, the bulb is so bright that it is given an opaque
coating internally.
 The light out put of incandescent lamps is about 10 to 15 lm/W. Thus:
- a 25W IL produces about 250 to 375 lm.
- a 40W IL produces about 400 to 600 lm.
- a 60W IL produces about 600 to 900 lm.
 The average lifetime of incandescent lamps is about 2000 hours when
operating at rated voltage.
 An incandescent lamp gives out light at all frequencies including DC.
 Incandescent lamps suffer from two disadvantages
- low efficiency and
- coloured light.
To overcome these drawbacks, the gaseous discharge lamp has been
developed.
 Fig 1.3 tungsten filament lamp

Discharge Lamps

When an electric current is passed through certain gases visible light is

produced. Gases are normally pure conductors especially at atmospheric
pressure, but applications of suitable voltage called, ignition voltage,
across the two electrodes can result in a discharge through the gas, which
is accompanied by electromagnetic radiation. The wavelength of the
radiation depends up on the gas, its pressure, and the metal vapour used
in the lamp. Although the current is small, a fairly high voltage is
required to maintain the discharge. For most discharge lamps the striking
voltage required is higher than the running voltage. So some means of
 limiting the running current is required. Argon gas and sodium vapour
are commonly employed in the manufacture of gaseous discharge lamps.

Colours of Discharge Lamps

The colour of the light emitted depends upon the type of gas used. The
colour obtained from some of the gases and vapours commonly employed
are listed in the table below

Electric discharge lamps can in general be classified as cold-cathode and

hot-cathode.

 Cold-cathode:
In some type of discharge lamp the electrodes are not heated. These types
are therefore known as cold cathode lamps, an example of this being the
ordinary neon tube.
 Uses a high voltage (3.5KV) for its operation.
 They are familiar as fluorescent tubes with 25mm in diameter, either
straight, curved, or bent to take a certain form for general lighting
purpose.
 The electrodes of these lamps are not preheated. e.g. Neon lamps.
 Hot-cathode:
In other type of discharge lamp the electrodes are heated, as this reduces the
voltage required to strike and maintain the discharge. Lamps using heated
electrodes are known as hot cathode lamps. A typical example is the
ordinary fluorescent lamp. The hot cathodes are usually in the form of short
filament which may be heated either by passing a heating current through it
or by the discharge current itself.
 Are commonly called fluorescent lamps.
  Are more commonly used type of discharge lamps.
 Available in tube lengths of 2.5m, 1.7m 1.3m or 30cm.
 Electrodes are heated and operating voltage is low or medium.
 To assist starting the mercury vapour is mixed with argon gas.
 Hot cathode lamps are produced as sodium vapour lamps, high-
pressure mercury vapour lamps, and fluorescent 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 connected through a high resistance. The auxiliary electrode is
used to start the discharge. A choke is provided to limit a current to a safe
value.
Fig.1.4 typical high-pressure mercury vapour lamps: (a) basic circuit (b)
modern mercury vapour lamp.

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. The high pressure mercury vapour lamp has an efficiency of
about 40-50lm/W they are manufactured in 250 and 400W ratings for use on
220-250v a.c. supply mains. Their application is mainly for industrial and
street lighting, commercial and display lighting.

Sodium vapour lamps:

Is a double glass container, the inner glass tube filled with Neon and Argon
gas and some sodium drops. When the supply is switched on, the lamp
would not start as the supply voltage is too low to start the discharge. The
leak transformer is connected across the mains produces a starting voltage of
about 400v. Then the Neon Argon gas starts the discharge, and afterwards
the sodium vaporizes and the discharge continues.
 Fig 1.5 sodium vapour
lamp

Fluorescent lamp (Low pressure mercury vapour lamps):

Certain materials, such as calcium halo phosphate, emit visible light
whenever they absorb ultra-violet light. This phenomenon is known as
fluorescence and may be used to produce a very efficient type of lamp. If a
tube of a discharge lamp containing mercury vapour is coated internally with
an even layer of fluorescent material a considerable proportion of the ultra-
violet light caused by the discharge is converted into useful visible light.
Low pressure mercury vapour lamps:
- consists of glass tube filled with mercury vapour at low pressure.
- is provided with two electrodes coated with electron emissive
material.
 - the inner wall of the tube is coated with fluorescent powder which
transforms ultraviolet radiation in to visible radiation or light.
 The light out put of fluorescent lamp is 70 lm/w and has an average
life of about 7500 hrs.
 The application includes lighting of shops, homes, factories, streets,
ships, transport (buses and trains), e.t.c.
 Using this tubes it is quite possible to achieve high lighting intensity
without excessive temperature rise and, owing to the nature of light
sources, the danger of glare is minimized.
 The efficiency of fluorescent lamp is about 40 lumens per watt, which
is about three times the efficiency of an equivalent tungsten filament
lamp.
Fluorescent tubes are available in the following sizes:

Fluorescent Lamp Circuits

Fig. 1.6 basic switch

starting circuits which operates as follows.
When the supply is switched on with the starter switch, s, closed a current
flows through the inductor, L, and through the lamp electrodes. The initial
current heat the lamp electrodes in readiness for striking the lamp. The
starting switch is now opened making a sudden interruption in the current
flowing through the inductor and so causing a high voltage to be
momentarily induced (Note that breaking an inductive circuit causes high
voltage to appear across the break in contacts, and energy is released in the
form of an arc. in this case, however, there is an easier way for the energy to
dissipate- via the gas, and the high voltage appears across the end of the
tube). This voltage starts a discharge between the two lamp electrodes and
the current rapidly rises to value determined mainly by the inductance of
inductor. The starter switch is left open while the lamp is a light, the
electrodes maintaining their operating temperature as long as they continue
to pass the discharge current. In practice it is desirable that the starter switch
should operate automatically, switching on when the supply is first on then
switching off to strike the lamp and remaining of all the time that the lamp is
alight. Due to the inductor the lamp current loges the supply voltage (at
approximately 0.5 p.f) a capacitor, C, is usually connected between the lamp
terminals to improve the overall power to an acceptable value.
 Starters
Three methods are commonly available for starting the discharge in a
fluorescent
tube: the thermal start, the glow start and the quick start.
A thermal starter consists of two contacts (one of which is a bimetal) and a
heater.
Fig.1.7 shows how such a starter is connected. When the supply to the lamp
is switched on, the heater is energized. Also, the lamp filaments are
energized via the starter contact. The heater causes the contacts to part and
the choke open circuits across the tube, so that discharge takes place.

Fig.1.7 thermal starter

The glow starter is the most popular of all the means of starting the
discharge. It comprises a pair of open contacts (bimetallic) enclosed in a
sealed glass bulb filled with helium gas. This assembly is housed in a metal
or plastic canister. Fig.1.8 shows how this type of starter is connected. When
the supply is switched on, the helium gas ionizes and heats up, causing the
contacts to close, and this energizes the tube filaments. As the contacts have
closed,
the discharge in the helium ceases, the contacts cool and part, open-
circuiting the choke across the tube and discharge takes place.

Fig.1.8 Glow starter

In the case of the quick start or instant starter, starting is achieved by the
use of an auto-transformer and an earthed metal strip in close proximity to
the tube(Fig.1.9). When the supply is switched on, mains voltage appears
across the ends of the tube, and the small part of the winding at each end of
the transformer energizes the filaments that heat up. The difference in
potential between the electrodes and the earthed strip causes ionization that
spreads along the tube.
Fig 1.9 Quick starter
 e

 Stroboscopic Effect
A 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. Although this effect is not noticeable to
the eye, machinery rotating at certain speed may appear to be stationary or
moving more slowly than it really is. This is known as the stroboscopic
effect and is obviously a cause of danger in situations such as workshops
where rotating machinery is in use.
a) If a three-phase supply is available the stroboscopic effect can be
minimized by connecting lamps to alternate phases. As the lamps in the
circuit attains their maximum and minimum values, the light output in
sequence of overall illumination is kept practically constant thereby keeping
the stroboscopic effect to a minimum.
b) If only a single-phase supply is available then the ‘lead lag’ circuit shown
in figure below may be used. In this circuit lamp A, is supplied via and
inductor and so has a lagging current, Both an inductor and a capacitor are
connected in series with lamp B. The inductor is required to supply the
initial starting surge. But, when the lamp is a light, the effect of the capacitor
predominates so that the lamp takes a leading current, It follows that when
one lamp is producing its minimum light output the other is producing its
maximum and so, by using this circuit the stroboscopic effect is greatly
reduced.

1.3. PRACTICAL LIGHTING SCHEMES

A good lighting system should produce uniform illumination of not less than
the required value. It should be free from glare and hard shadows. In fact
and endeavour should be made to have quality of light as close to day light
as possible. The interior lighting schemes may be classified as: -
i. Direct light
ii. Semi- direct lighting
iii. Semi-indirect lighting
iv. Indirect lighting and
v. General lighting
1. Direct light: - the most commonly used type of lighting scheme. In this
scheme more than 90% of total light flux is made to fall directly on the
working plane with the help of deep reflectors. Though it is more efficient
but causes hard shadows and glare. It is mainly used for industrial and
general out-door lighting.
2. Semi-direct lighting: - in this lighting scheme 60-90% of the total light
flux is made to fall down wards directly with the help of semi-direct
reflectors. The remaining light is used to illuminate the ceiling and walls.
Such a lighting scheme is best suited to rooms with high ceiling where there
is a high level of uniformity of illumination is desired. Besides this scheme
avoids glare, it also improves the efficiency of the system with reference to
the working plane.
3. Semi indirect lighting: -in this scheme 60-90% of total light flux is
thrown up wards to the ceiling for reflection and the rest reaches the working
plane directly except for some absorption by the bowl. This lighting scheme
has soft shadows and is glare free. It is mainly used for indoor decoration
purpose.
4. Indirect lighting scheme: - in this scheme more than 90% of total light
flux is thrown upwards the ceiling for diffuse reflection by using inverted or
bowl reflector. In this scheme the glare is reduce to minimum. The resulting
illumination is soft and more diffused. The shadows are less prominent and
the appearance of the room is much improved. It is used for decoration
purpose in cinemas, theatres and hotels etc. and in areas where troublesome
shadows are produced if direct light in lighting is employed.
5. General lighting: - in this scheme lamps made of diffusing glass are used,
which gives nearly equal illumination in all directions. All fittings may be
reduced to five basic types according to their light distribution as shown in
Fig

Fig 1.10 a) Type of reflectors b) Lighting fittings, types and performance

 Design of lighting schemes

The lighting scheme should be such that it may,
I. provide adequate illumination
II. provide light distribution all over the working plane as uniform as
possible
III. Provide light of suitable colour.
IV. avoid glare and hard shadows as far as possible

1. Illumination level: - In order to see the details of the things that surround
us the source has to illuminate them very well in order the objects take the
necessary brightness. For each type of work there is a range of brightness
most favorable to output in terms of quality and quantity.
Degree of illumination, to give necessary brightness to objects, depends
upon:
 I. the size of the object and distance of the observer.
II. contrast between the object and background. Greater the contrast
greater will be the illumination required to distinguish the object
properly.
III. speed of object - Speedy object require more illumination.
IV. duration of gazing - Object seen for long duration of time require
more Illumination .
2. Uniformity of Illumination: - It has been found that visual performance is
best if the range of brightness within the field of vision is not greater than
3:1, which can be achieved by employing general lighting in addition to
localized lighting. Otherwise due to the frequent accommodation of pupil or
iris of the eye, fatigue is caused and it creates psychological felling of
loneliness, gloom and unfriendliness.
3. Colour of light: - The appearance of the body colour entirely depends
upon the colour of the incident light. In general the composition of the light
should be such that the colour appears natural.
4. Shadows: - In lighting installation, formation of long and hard shadows
causes fatigue and are undesirable. However a certain amount of shadow is
desired as it helps to give shapes to solid objects and make them easily
recognised. But there is one exception to this i.e. in drawing offices, where
we are to see flat surfaces. Hard and long shadow can be avoided by:
a) rising a large number of luminaries mounted at a height not less than
2.5m.
b) by using wide surface of light - using globes or indirect lighting system.
5. Glare: - Glare is generally produced by very bright sources of light, which
emit light directly or at very low angle towards the viewer. This causes the
person to neglect the other surrounding objects, as they appear darker and is
a major cause of road accidents. The glare is also caused by highly polished
surfaces when the angles are incorrect. This also tends to damage retina of
the eye. Glare may be direct or indirect. Motorcar headlights produces direct
glare.
In other words glare may be defined as the brightness within the field of
vision of such a character as to cause annoyance, discomfort interference
with the vision or eye fatigue. Therefore, glare is to be avoided at any cost.
For this purpose very bright point sources of light should be avoided. Highly
reflective surfaces should be replaced by Mat surfaces, which cause
diffusion. The angle of light should be such that it does not dazzle the
person. A surface, which is almost free from mirror reflection, is called a
mat surface. The factories act discusses the matter and lays down regulations
to prevent it. If a glare is produced by a lighting point, such as incandescent
lamp, it can be avoided by the use of globes or making the light source at
such ba height that to place them above the ordinary range of vision. In
fulfilling the above requirements, in designing a good lighting scheme, we
have to consider
i. The intensity of illumination required
ii. The selection of the required lamps and fittings
iii. The size of the room
iv. The conditions under which the illumination is used etc
The recommended illumination level for various occupancies is shown in
Tables given on page and subsequent. The choice of lamps for different
type of occupancies differs. Tubular fluorescent and tungsten filament lamps
can be used when lighting is to be done in small premises. But in large
premises, the lighting can be carried out by using high intensity sources such
as mercury or sodium discharge lamps. The following are some of the
conditions that should be considered when the illuminations are used:
► Utilization Factor (ηB) - the whole light radiated by the lamps doesn’t
reach the working plane. The ratio of lumens reaching the working plane to
the total light given out by the lamp or lamps, when the installation is new,
is known as utilization factor or coefficient of utilization. The value of
utilization factor depends upon
I. the mounting height of lamps
II. area to be illuminated
III. type of lighting scheme
IV. colour of the surrounding, etc.
► Spacing Luminaries: - correct spacing is of great importance to provide
uniform illumination over the whole area. The ratio of the horizontal spacing
between rows to the height of the luminaries above the working plane, called
space to height ratio, depends quite on luminous output, type of lighting
scheme and on the extent of candlepower distribution curve of the laminar.
Mounting height is largely governed by the type of the building and type of
lighting scheme employed. The term “general lighting” implies that the
illumination at the working level should not vary substantially throughout
the room. Therefore it is apparent that the fitting for general lighting should
not be so placed that the illumination received from each fitting overlaps and
builds up that of its neighbors. That means the distance lights source from
the wall should be equal to one half of the distance between two adjacent
light sources. Also distance between lighting fittings should not exceed 1.5
times the mounting height.
In the case of direct and semi-direct luminaries, it is generally advisable to
mount them high considering a normal ceiling height and average size floor
area. With fluorescent luminaries it is good practice to aim at a value of
unity for this ratio and to set on upper limit of 3/4. In the case of indirect and
semi-indirect luminaries, it is a good practice to aim at a horizontal spacing
between rows approximately equal to the height of the ceiling above the
working plane, and in no case should the horizontal spacing exceed 11/3
times this height.
► Colour of Surrounding Walls: - the illumination in a room depends upon
the light reflected from walls and ceilings. White walls and ceilings reflect
more light as compared to collared ones.
► Maintenance Factor - as we are to continue to use the installation, the
illumination produced considerably decreases due to ageing of the lamps and
accumulation of dusts on the lamps, reflectors, ceiling and walls. Its value is
more if there is much as the ageing problem increases, etc. The value is
mostly ranges between 0.8 and 1. The other term used is depreciation factor,
which is merely the inverse of the maintenance factor. Its value is more than
unity.

Methods of lightning calculation

In order to estimate the number and the type of light fittings required to suit
bba particular environment, it is necessary to know what level of luminance
is required, the area to be illuminated, the maintenance factor and the
coefficient of utilization, and the efficiency of the lamps to be used. A
number of methods have been employed for lighting calculations among
which may be mentioned:
A. Watts per square meter method
B. Lumen or Light flux method
► Watts per Square Meter method: - applicable for rough calculations. It
consists in making an allowance of watts per square meter of area to be
illuminated accordingly to the illumination desired on the assumption of the
average figure of an overall efficiency of the system. According to NEC
220-3(d) this figure is about 3 watt per ft2.
Example: - A house has an external dimension of 30ft by 50ft. If an 80w
fluorescent lamps, and 220V supply is used, determine the size of the service
wire and the number of lamps required.
Solution:
A = 30ft X 50ft
= 1500ft
Total wattage required = 1500 X 3w = 4500w ⇒ 4.5Kw
No of lamps required = 4.5Kw/80w = 56.1
⇒ 56 lamps - each 80w
Current carrying capacity = 4.5Kw/220V = 20.5A
Therefore, the size of the cable will be conductor if there is no any
correction factor.
► Lumen or Light flux or efficiency method: - it is the most advisable
method to be used. Lumens' reaching the working plane is calculated as:
Required Level of Illumination in the room= Total flux output of the lamps
in the room * Correction Factor
Total area of the
room
Required Level of Illumination in the room = No. of Fixture * Flux output
per Fixture * Correction Factor
Total area
of the room

Required Level of Illumination in the room

= No. of Fixture * No. Lamp per Fixture * Flux output per lamp *
Correction Factor

Total area of the room

Correction Factor = Utilization Factor * Maintenance Factor

Thus E = N * n * фL * UF * MF
A

N= A*E
n*фL*UF*MF

For New Installation we have the following

N = 1.25 * A * E
n * фL * UF * MF,

Where
E – Required Illumination level
A - Working surface in m2
φL - Luminous flux of one lamp in lm

UF - Utilization factor
MF- Maintenance Factor

exercises : -
1. A road 300 m long is required to be illuminated by providing 40W
fluorescent lamps. The width of the road is 4m. Design a street lighting
scheme for obtaining minimum level of illumination of 0.6 lux assuming a
mounting height of 9m and a 0.5 coefficient of utilization. (In designing you
have to determine the distance between the poles and find out the number of
poles required for the given distance.)
2. A light assembly shop, 15m long, 9m wide and 3m up to trusses, is to be
illuminated to a level of 200 lux. The utilization and maintenance factors are
respectively 0.9 and 0.8. Make a scale drawing of the plan of the shop and
set out the required lighting points, assuming the use of tungsten lamps and
dispersive metallic reflectors. You may assume a lamp efficiency of 125
lm/W, and spacing height ratio of unity.
3. A hall 30m X 15m height is to be provided with a general illumination of
120 lm/m2 taking a coefficient of utilization of 0.5, depreciation factor 1.4
and appropriate space height ratio, determine the no. of fluorescent tubes
required, their spacing, mounting height and total wattage. Take luminous
efficiency of fluorescent tubes as 40lm/W for 80-watt tube.
CHAPTER 2
WIRING MATERIALS AND ACCESSORIE

In order to assemble properly and intelligently the great number of available

electrical materials, devices, fittings, and equipment to form a complete
wiring system, we must understand the basic principles regarding them.

2.1 WIRE AND CABLES

The term wire and cable are used more or less synonymously in house
wiring. Strictly speaking, single wire, may be bare or covered with
insulation is known as a wire and several wires stranded together is known
as a cable. But in practice bare conductors, whether single or stranded
together are termed as wire and conductors covered with insulation are
termed as cables.
The necessary requirements of a cable are that it should conduct electricity
efficiently, cheaply, and safely. This should neither be so small so as to have
a large internal voltage drop nor be too large so as to cost too much. Its
insulation should be such as to prevent leakage of current in unwanted
direction and to minimize risk of fire and shock.

A cable consists of three parts:

a) the conductor or core- the metal wire or strand of wires caring current.
b) the insulation or dielectric- a covering of insulation material to avoid
leakage current from the conductor.
c) the protective covering- for protection of insulation from mechanical
damage.

2.2 CONDUCTOR MATERIALS USED IN CABLES

Copper and aluminum are the materials used as conductors in power and
lighting cables.
1. Copper: though silver is the best conductor, but due to its higher cost it is
hardly used anywhere. The next best conductor is copper, which is
comparatively cheap.
The electrical resistivity of pure copper at 200c is 1.786 x 10-8 ohm .m. It is
mechanically strong, hard, extremely tough, durable and ductile. It is highly
resistive to corrosion, oxidation, and pitting.
2. Aluminum: is frequently used in place of copper for bare electric cables
used for long distance power distribution. The electrical conductivity of
aluminum is about 60% of that of copper. The only application of aluminum
cables for wiring in buildings is for a continuous bus-bar system of
distribution, used sometimes in blocks of flat or office buildings for rising
mains and sub mains of large sectional area.

2.3 INSULATING MATERIALS

The insulating material used in electric cable must possess the following
properties.
• High resistivity
• High flexibility
• Non-in flammability
• High resistivity to moisture, acid or alkalis qualities. So the type of
insulating materials used depends up on the service for which the cable is
required.

►Various types of insulating materials used in cables are:

1) Rubber
2) PVC.
3) Vulcanized Indian Rubber
4) Impregnated paper

2.4 TYPES OF CABLES USED IN INTERNAL WIRING

The wires used for internal wiring of buildings may be divided in to different
groups according to:
- The type of conductor
- The number of cores
- The voltage grading
- The type of insulation used.
According to the number of cores, the cables may be divided in to classes
known as single core, twin core, twin core with ECC (earth continuity
conductor).
According to voltage grading the cables may be divided in to two classes:
250/440 volt and 650/1100-volt cable.

►According to type of insulation cables can be classified in to:

1. Vulcanized Indian Rubber (VIR) cables:
-VIR cables are available in 250/440volt as well as 650/1100 volt grades and
are used for general conduit wiring.
2. Lead sheathed cables:
• available in 250/440 volt grade
• are used for internal wiring where climatic condition has moisture.
• Is a vulcanized rubber insulated conductor covered with a continuous
sheath of lead .The sheath provides very good protection against the
absorption of moisture and sufficient protection against mechanical injury
and can be used with out casing or conduit system.
• It is available as single core, flat twin core, flat three core and flat twin core
with ECC.
3. PVC cables:
• Are available in 250/440 volt and 650/1100 volt grades
• Used in concealed type of wiring system.
• Since PVC cables are harder than rubber, they do not require cotton taping
and braiding over it for mechanical and moisture protection.
4. Weather proof cables:
•Are used for out door wiring and for power supply
• are not affected by heat or sun or rain.
• Are either PVC insulated or vulcanized rubber-insulated conductors being
suitably taped (only incase of vulcanized rubber insulated cable) braided and
then compounded with weather resisting material.
•Are available in 250/440 and 650/1100 volt grades.
5. Flexible cords and cables:
- It consists of wires either silk or cotton or plastic covered, plastic cover is
more popular as it is available various pleasing colors. Flexibility and
strength is by using conductors having large number of strands.
- Most stranded conductors are built upon a single central conductor,
surrounding this conductor are layers of wires in a numerical progression of
6 in the first layer, 12 in the second layer, 18 in the third layer and so on.
►Colors of conductors:
Color identification of bare conductors and cable cores are given by
EELPA’S regulation
Earthling --------------------------------------------- white
Live of a.c single-phase circuit ------------------- Green
Neutral of ac single or three phase ac circuit ----black
Phase R of three-phase ac circuit ------------------Green
Phase S of three-phase ac circuit ------------------ Yellow
Phase T of three-phase ac circuit ------------------ Red

►General specification of cables:

The complete specification of a cable will give the following information:
i. The size of the cable
ii. The type of conductor used in cables (copper or aluminum)
iii. Number of cores that the cable consists of (single core, twin core, twin
core with ECC etc,)
iv. Voltage grade
v. Type of insulation (taping, braiding & compounding)

2.5 CONDUITS
The commonest method of installing cables is to draw them in to a conduit.
The conduit can be steel or plastic steel conduit is made in both light gauge
and heavy gauge of which heavy gauge is much more frequently used. In
general, conduits can be classified as:
i. Light gauge steel-plain (unscrewed) conduit.
ii. Heavy gauge steel-screwed conduit.
iii. Flexible conduit
iv. PVC conduit.

I. Light gauge steel conduit:

• This type of conduit is used with special grip fittings.
• It is available with an external diameter of 12mm, 16mm19m, 25mm,
31mm, 38mm, and 50mm. In general, light gauge is the cheapest and
quickest of conduit installations but should be used where the location is dry
and there is little likelihood of mechanical damage.

ii. Heavy gauge screwed steel conduit:

• Though it is very expensive, this type of conduit provides a permanent
installation with a maximum of protection for the cables
• The joints into fittings are by means of screw threads which provide
mechanical strength and good electrical conduit:
•Are available in approximately 3meter lengths and are threaded at the two
ends.

iii. Flexible steel conduit:

• This usually consists of light galvanized steel strip spirally wound, and to
some extent, interlocked, so as to form a tube.
• It is made in size from 19mm to 50mm internal diameter and in two
grades: non water tight and water tight.
• Available in lengths up to 250 meters. So no coupling is required ands
hence no threading.
• Since the conduits are flexible and are easily bent no elbow is required.
• One of the most common uses of flexible conduit is for protecting the final
connections to motors. It has the additional advantage of reducing the
transmission of vibration. However, the flexible conduit is costlier than the
rigid conduit.

Iv. PVC conduit: This type of conduit wiring is finding wide applications in
internal wiring because it is light in weight, shock proof, anti-termite, fire
resistant, acid and alkaline resistant. Can be used for surface, recessed or
concealed type of wiring.

2.6 CONDUIT ACCESSORIES AND FITTINGS

► Conduit couplers:
- used to join two lengths of conduit
- are threaded on both ends.
► Bends elbows and tees: - are generally called conduit fittings.
Bends are usually used for change in direction of conduit. This should never
be sharp. The minimum allowable radius of curvature is 2.5 times the
outside diameter of the conduit.
Solid elbows and tees should be used only at the end of the conduit run (e.g.
close behind a light fitting or accessory.).
► Conduit boxes
- are used in surface conduit wiring as well as concealed conduit wiring.
- are of different designs which serve the following purposes:
i. For providing connections to light, fan, and other points.
The conduit boxes serving the purpose are known as outlet boxes because
conduit terminates at the boxes.
ii. For pulling of cables in to the conduits. The boxes serving this purpose
are known as inspection boxes.
iii. For housing junction of cables. The conduit boxes serving this purpose
are known as junction boxes.
2.7. LIGHTING ACCESSORIES AND FITTINGS
► Switches:
-Are used to control lighting circuits.
- Most are rated at 5/6A, but ratings at 15A are also available.
-Are available in three types: single pole, two-way and four-way
(Intermediate) each for control of a practical circuit arrangement.
To allow true control of a number of different circuits from one position,
switches are contained within the same unit: two-gang, six-gang, etc.
* Single chord ceiling switch is suitable for installation in the bathroom,
where by one pull of the chord puts the switch ON and the following pull
puts the switch off.
* Switches for water-heaters are of the double pole type and rated to carry
20A.
Are also available at 32A and 45A rating, the latter being used to control
cooker circuits.
* Dimmer switches are used to allow control of the level of lighting from
luminaries.
* Splash-proof switches are found in situations where water is present, such
as in shower rooms.
► Lamp Holders
* Are designed for quick removal and replacement of the lamp and yet they
must hold the lamp in firm metallic contact to prevent overheating.
* There are three main sizes of lamp holders: Bayonet-cap (B, C), the
medium Edison screw (E.S) and the Goliath screw (G.E.S).
* For ordinary tungsten filament lamps up to 200W the lamp caps and lamp
holders are B, C, caps, up to 300W the caps are E.S, and above 300W they
are G.E.S. In any case where the lamp is to be installed, the appropriate size
and type of holder must be fitted. Lamp holders may be either the insulated
type of Bakelite or the brass type with porcelain interior.

► Plugs and socket outlets:

These are used to enable portable apparatus to be connected to the fixed
wiring and comprises of two or three contact tubes and terminals. The plug
is the movable part connected to the apparatus by flexible wire, and consists
of two or three contact pins to fit in to the contact tubes.

2.8 FUSES
* Consists of a piece of copper or tin-lead alloy wire, which will melt when
carrying a predetermined current. This element with contacts, carrier and
base is called a fuse.
* Is placed in series with the circuit to be protected, and automatically
breaks the circuit when over loaded.
* The time for blowing out of a fuse depends on the magnitude of excess
current. i.e. the larger the fault current the more rapidly the fuse blows.
* Three terms are used in connection with fuses.
Current rating: this is the maximum current that a fuse will carry
indefinitely without undue deterioration of the fuse element.
Fusing current: this is the minimum current that will ‘blow’ the fuse.
Fusing Factor: this is the ratio of minimum fusing current to the current
rating
Fusing Factor = minimum fusing current ≥ 1

* There are two main types of fuses: the rewritable and the cartridge (or high
breaking capacity, HBC) fuses; the high breaking is a development of the
cartridge type.
► Rewritable Fuses
* This type of fuse consists of a porcelain (usual material) bridge and base.
The bridge has two sets of contacts, which fit in to other contacts in the base.
The fuse element usually tinned copper wire is connected between the
terminals of the bridge. An asbestos tube or pad is usually fitted to reduce
the effects of arcing when the fuse element melts.
* The rewritable fuse is a simple and relatively cheap type of over current
Protective device and is still widely used despite several disadvantages
including:
a. The fact that it is rewirable enables the wrong size of the fuse wire
(element) to be used.
b. Undue deterioration of the fuse element due to oxidation.
c. Lack of discrimination. This means that normal starting surges (e.g. when
motors, etc are switched on) are “seen” by the fuse as an over load and will
there fore break the circuit.
d. Damage, particularly in conditions of severe short circuit.
* The fusing factor for a rewirable fuse is about 2.

► Cartridge (or High Rapture Capacity, HRC) Fuses

The obvious disadvantages of rewirable fuse led to the development and use
of the cartridge type fuse. The fusing factor of the cartridge type fuse is
about 1.5.
The high breaking capacity fuse (HBC) has its fusing characteristics
carefully controlled by the manufacturer. As its name implies it can safely
interrupt very large currents. The fuses are often used to protect large
industrial load and main cables. The cartridge barrel is of high-grade
ceramic able to with stand the shock conditions when a heavy fault current is
interrupted. Except for very low ratings, the fuse element is made from pure
silver. The filler is powdered silica, carefully dried before use. An indicator
is provided to show when the fuse has blown.
The cartridge type (HBC) fuse is more expensive than the rewirable. The
fusing factor of HBC fuse is for small loads up to 1.25A, thus a 10 A HBC
fuse will blow at 12.5A. HBC fuses are discriminating; which means that
they are able to distinguish between a starting current taken by a motor
(which lasts for a matter of seconds) and a high fault or overload current
(which lasts longer). Motors are normally protected against overloads by the
starter trip; the fuses are required only to give protections against short
circuit currents and overloads outside the capacity of thermal trip.

2. 9 CLRCUIT BREAKERS
Is a device designed to open and close a circuit by non- automatic means
and to open the circuit automatically on a predetermined over-current with
out injury to itself when properly applied within its rating. So a circuit
breaker is a combination device composed of a manual switch and an over –
current device

A circuit breaker has several advantages over any type of fuse

a. In the event of fault or overload all the poles are simultaneously
disconnected from the supply
b. overload and time-lags are capable of adjustment within limits
c. the circuit can be closed again quickly onto the fault safely
Essentially a circuit breaker consists of a carefully calibrated bimetallic strip.
As current flows through the strip, heat is created and the strip beds. If
enough current flow through the strip, it bends enough to release a strip that
opens the contacts, interrupting the circuit just as it is interrupted when a
fuse blows or a switch opened. In addition to the bimetallic strip that
operates by heat, most breakers have a magnetic arrangement that open the
breaker instantly in case of short circuit. A circuit breaker can be considered
a switch that opens itself in case of overload.
Circuit breakers are rated in amperes just as fuses are rated. Like fuses,
breakers are tested in open air to carry 110% of their rated loads indefinitely
without tripping. Most breakers will carry 150% of their rated load for
perhaps a minute, 200% for about 20 sec. and 300% for about 5 sec, long
enough to carry the heavy current required to start most motors.
► Standard ratings: both fuse and circuit breakers are available in standard
ratings of 6,10, 16, 20, 25, 35, 50, 63, 80, 100, 125, 160, 224, 250, 300, and
large sizes.

2.10. DISTRIBUTION BOARD

A distribution board is an assemblage of parts, including one or more fuses
or circuit breakers, arranged for the distribution of electrical energy to final
circuits or to other sub distribution boards. It consists of a case inside which
is a frame holding a number of fuse (CB) carriers behind the frame or some
thing along side or above it, is a bus-bar to which the incoming sub-main is
connected. From the bus-bar there is connection provided to one side of each
fuse way (CB). The installer to the out going terminal of the fuse ways then
connects each final sub-circuit
The standard distribution boards usually have 4, 6, 8, 12, 18 or 24 fuse ways
both single phase and three phases are available. It is not necessary to utilize
all the available fuse ways on a board, and in fact it is very desirable to leave
several spare ways on each board for future extension.