Page 328 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Types of lamp

1 Incandescent lamp (By passing a current through a filament).
2 Gas discharge lamp (By electric discharge through vapors or gases).
3 Arc lamps (By developing arc between two electrodes).
4 LED.

Filament or incandescent lamp
Working Principle:
As we know when a room heater is switched On, it gives out red light with heat at the working temperature of
750°C and at this temperature the radiations are mostly in infra-red regions. This working principle is used to
develop the filament lamp.
Filament or Incandescent Lamp
When an electric current is passed through a fine metallic wire, it raises the temperature of wire. At low temperature
only heat is produced but at higher temperature light radiations goes on increasing. As filament lamp consists
of fine wire of high resistive material placed in an evacuated glass bulb. This type of lamps are operated at the
temperature of 2500°C .
Properties of metal for filament
1 High melting point: so that it can be operated at high temperature.
2 High specific resistance: so that it produces more heat.

3 Low temperature coefficient: so that filament resistance may not change at operating temperature.
4 Low vapor pressure; so that it may not vaporize
5 High ductile: so that it may withstand mechanical vibrations
Carbon filament lamp

It is generally used for heating purpose. The filament is of carbon. Melting point of carbon is 3500 degreeCelsius.
Working tem: is 1800.

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CITS : Power - Electrician & Wireman - Lesson 54-59 CITS : Power - Electrician & Wireman - Lesson 54-59