uept unit 1

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UTILIZATION OF ELECTRIC POWER
AND TRACTION
LIGHT
Light is defined as electromagnetic radiation that is capable of
affecting the sense of sight.
LIGHTNING FACTS




We spend about one-quarter of our budget on lighting.
Technologies developed during the past 10 year helps
us to cut lighting costs to 30% to 60% while enhancing
lighting quality and reducing environmental impacts
In typical house lightning accounts for 10% of total
electricity bill and in case of office it accounts for 45%
of electricity bill
Inefficient lightning also gives lot of heat leading to
increased need for air conditioning
The electromagnetic spectrum spreads over a tremendous range of
frequencies or wavelengths. The wavelength l is related to the
frequency f:
c = fl
c = 3 x 108 m/s
Those EM waves that are visible (light) have wave-lengths that range from
400 nm to 700 nm .
Red, l
0.00007 cm
Violet, l
0.00004 cm
Frequency
f (Hz)
wavelength
102
l ( nm)
4
102
3
Gamma rays
102
2
102
1
102
010
191
018
101
710
16
101
510
141
013
101
210
111
010
109
X-rays
Ultraviolet
Infrared
rays
Short Radio
waves
Broadcast Radio
Long Radio
waves
10-7
10-6
10-4
10-3
10-1
1
10
102
103
104
105
106
107
108
109
101
010
111
012
101
3
A wavelength of one
nanometer 1 nm is:
1 nm = 1 x 10-9 m
Visible Spectrum
400 nm  700 nm
Red 700 nm  Violet 400 nm
c = fl
c = 3 x 108 m/s
Human eyes are not
equally sensitive to
all colors.
555 nm
Sensitivity
Eyes are most sensitive in
the mid-range near
i.e when l = 555 nm.
Sensitivity curve
400 nm
700 nm
Wavelength l
40 W
40 W
Yellow light appears brighter to the eye
than does red light.
Luminous
Flux ‘F’- It is defined as total
amount of light emitted per second from a
luminous body. Unit- lumen
Illumination
‘E’ -The distribution of light on
a horizontal surface is called its illumination.
Luminous
intensity -The luminous intensity
for a light source is the luminous flux per
unit solid angle.
F
I



F
I

Solid angle-A solid angle of one steradian (1 sr) is subtended at the
center of a sphere by an area A equal to the square of its radius (R2 ).
R
A

The
Steradian

A
R2
The illumination E of a surface is directly
proportional to the intensity I and inversely
proportional to the square of the distance R.
F
F
E  ; I  ; F  I
A


I
A
E
but   2 so that
A
R
Area A
I
Illumination, E  2
R
R
This equation applies for
perpendicular surfaces.
R
A

A
The
 2
Steradian
R
Total flux: F = 4pI
Luminous intensity:
F
I

Unit is the candela (cd)
F
E
Unit: lux (lx)
A
I. Inverse Square Law : The Illumination of a surface
is inversely proportional to the square of the
distance of the surface from the source.
Where d is the distance from the light source.
2. Lambert’s Cosine Law : Lambert’s cosine
law states that the illuminance falling on any
surface depends on the cosine of the light’s
angle of incidence, θ.
I) Direct Lighting



90 – 100% of light output of the lamp falls towards
downward.
widely used for industrial and outdoor lighting
scheme is more efficient but suffers from hard shadows and
glare
II )Semi-direct Lighting



60-90% of the total is made to fall downwards directly by
using reflectors
rest of the light is used to illuminate the walls and ceilings.
This scheme is employed in rooms with high ceilings.
III) Indirect Lighting Scheme





Output of the lamp is directed upward to the ceiling and upper
side of walls.
Reflected back to the working plane area.
Entire ceiling becomes primary source of illumination.
Lighting is highly expensive and has zero eye strain.
Ideal lighting system for computer Centre and software industry.
IV) Semi-indirect Lighting Scheme



60-90% of light from the lamp is thrown upwards to the ceiling
and remaining flux reaches the working surface.
Glare is completely eliminated in this.
It is used for indoor lighting decoration purpose.
1.
2.
3.
4.
5.
Intensity of illumination : The amount of lumen required
in factories, offices, schools/colleges, hospitals etc.
Selection of luminaires (light fitting)
Size of the room : Utilization factor is taken into account
depending on the lumen output of the fitting, size and
shape of the room, height of ceiling etc.
Mounting height and spacing of fittings :The distance of
the light source from the wall should be equal to one
half the distance between two adjacent light sources.
Also the distance between light fittings should not
exceed 1.5 times the mounting height.
Conditions of use : To account for dirt/dust and
deterioration of lamp efficiency, the terms maintenance
factor and depreciation factor are taken into account.






Fixture efficiency
Lamp lumen output
The reflectance of surrounding surfaces
The effects of light losses from lamp lumen
depreciation and dirt accumulation
Room size and shape
Availability of natural light (daylight)
There are three basic types of lighting:
1. Incandescent
2. Fluorescent
3. Discharge Lamp

Filament
Light is produced
by a tiny coil of
tungsten wire that
glows when it is
heated by an
electrical current.
◦ shortest live
◦ Inefficient

Standard incandescent

Tungsten halogen

Reflector lamps
◦ Most common yet the most inefficient
◦ Larger wattage bulbs have a higher efficacy than smaller
wattage bulbs
◦ It has a gas filling and an inner coating that reflect heat
◦ Better energy efficiency than the standard bulb
◦ Reflector lamps are designed to spread light over specific
areas
◦ floodlighting, spotlighting etc




Fluorescent lamps last about 10
times longer than incandescent
bulbs
Fluorescent lights need ballasts
(i.e., devices that control the
electricity used by the unit) for
starting and circuit protection
filled with an argon and a small amount of mercury
coated on the inside with phosphors
equipped with an electrode at both ends 3 to 4 times as efficient as
incandescent lighting
Fluorescent lamps provide light by the following process:
◦ An electric discharge (current) is maintained between the
electrodes through the mercury vapor and inert gas.
◦ 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




CFLs can replace
incandescent lamps
that are roughly 3 to 4
times their wattage
They last 10 to 15
times as long.
Cost from 10 to 20
times more than
comparable
incandescent bulbs
One of the best
energy efficiency
investments available.


1.
2.
3.

1.
2.
An electric current is passed
through a gas or vapor to give
luminous
Color of light depends upon
nature of gas
Neon discharge –orange red
light
Mercury vapour – blue light
Sodium vapour- orange yellow
light
Type of discharge lamp
Type-1 : colour of light is same
as discharge through lamp
Type -2 :- Use the
phenomenon of flurorescene
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