2. • Necessity of Illumination
• A human depends on Light for all activities. Light
is a natural phenomenon, very vital for existence,
which is taken for granted. In fact, Life involves
day night cycles beginning with sunrise and
ending with sunset. Pre-historic man had activities
limited only to day time.
5. • Inverse square law
• The inverse square law defines the relationship
between the irradiance from a point source and
distance. It states that the intensity per unit area varies
in inverse proportion to the square of the distance.
• Lambert’s Cosine Law
• The irradiance or luminance falling on any surface
varies as the cosine of the incident angle, The
perceived measurement area orthogonal to the
incident flux is reduced at oblique angles, causing
light to spread out over a wider area than it would if
perpendicular to the measurement plane.
13. TYPES OF LAMPS
1. Incandescence
2. Mercury vapour lamp
3. sodium-vapour lamp
4. neon-gas lamp and
5. fluorescent lamps
6. LED lamp
14. • INCANDESCENT LAMPS
• Incandescent lamp technology uses electric
current to heat a coiled tungsten filament to
incandescence. The glass envelope contains a
mixture of nitrogen and a small amount of other
inert gases such as argon. Some incandescent
lamps, such as some flashlight lamps, also contain
xenon. Some of these incandescent lamps are
called xenon lamps, but are not the same as the
high-pressure xenon lamps Incandescent lamps
have come a long way since Thomas Edison's first
carbon filament lamp, which, when introduced in
1879, had a life of about 40 hours.
15. • Halogen Lamps
• Unlike incandescent lamps, halogen lamps use a
halogen gas fill (typically iodine or bromine),to
produce what is called a “halogen cycle” inside
the lamp. In the halogen cycle, halogen gas
combines with the tungsten that evaporates from
the lamp filament, eventually re-depositing the
tungsten on the filament instead of allowing it to
accumulate on the bulb wall as it does in standard
incandescent lamps.
16. • Discharge Lamps
• In all discharge lamps, an electric current is
passed through a gas or vapour which renders it
luminous. The elements most commonly used in
this process of producing light by gaseous
conduction are neon, mercury and sodium
vapours.
17. • SODIUM VAPOUR LAMPS
• It consists of an inner U-tube A made of a special
sodium-vapour-resisting glass. It houses the two
electrodes and contains sodium together with the
small amount of neon-gas at a pressure of about
10 mm of mercury and one percent of argon
whose main function is to reduce the initial
ionizing potential.
18.
19.
20. • FLUORESCENT LAMPS
• Fluorescent lighting accounts for two-thirds of all
electric light in the United States. The fluorescent
lamp is a gas discharge source that contains
mercury vapour at low pressure, with small
amount of inert gas for starting. Once an arc is
established, the mercury vapour emits ultraviolet
radiation.
21. • STREET LIGHTING
• Road lighting provides visual conditions for safe,
quick and comfortable movement of Road users.
• The factors responsible for the lighting scheme
for roads are:
i. Luminance Level.
ii. Luminance Uniformity.
iii. Degree of Glare limitation.
iv. Lamp Spectra and
v. Effectiveness of visual guidance.
22. • ENERGY SAVING LAMPS
• Electric lighting is a major energy consumer.
Enormous energy savings are possible using
energy efficient equipment, effective controls,
and careful design. Using less electric lighting
reduces heat gain, thus saving air-conditioning
energy and improving thermal comfort.
Electric lighting design also strongly affects
visual performance and visual comfort by
aiming to maintain adequate and appropriate
illumination while controlling reflection and
glare.
23. • LED (Light Emitting Diode)
• The LED has to be structured so that the photons
generated from the device are emitted without
being reabsorbed. One solution is to make the p
layer on the top thin, enough to create depletion
layer. Following picture shows the layered
structure. There are different ways to structure the
dome for efficient emitting
24. • Advantages of using LEDs
• LEDs produce more light per watt than
incandescent bulbs; this is useful in battery
powered or energy-saving devices.
• LEDs can emit light of an intended colour
without the use of colour filters that traditional
• lighting methods require. This is more efficient
and can lower initial costs.
