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Tungsten Halogen Lamp – Construction, Working and Applications
A tungsten halogen lamp, also called halogen lamp, is a developed tungsten filament lamp. The halogen lamp consists of a tungsten filament that is enclosed in an environment of an inert gas and a small quantity of a halogen such as bromine or iodine.
The combination of the tungsten filament and halogen results in a chemical reaction known as halogen cycle, which increases the life of the filament and eliminates the drawbacks of an ordinary filament lamp.
The halogen lamp was developed by E. G. Fridrich and E. H. Wiley in 1958 by introducing a halogen gas inside the incandescent lamp. The working principle of the halogen lamp is based on the halogen cycle.
Construction of Halogen Lamp
The construction of a typical tungsten halogen lamp is shown in the figure.
A tungsten halogen lamp consists of a filament made up of tungsten and housed in a fused silica quartz glass bulb. The glass bulb is filled with an inert gas like argon and a small amount of halogen like bromine or iodine. Two terminal leads are taken out from the lamp for electrical connection.
Working of Halogen Lamp
The tungsten halogen lamp works on the principle of halogen cycle. It works as a thermal radiator, i.e. light being generated when a solid is heated to a very high temperature. Thus, for a halogen lamp, the brightness of the light is proportional to the heating temperature.
When an electric current flows through the tungsten filament lamp, heat is produced which increases the temperature of the tungsten filament and causes the emission of light. Because of the very high temperature, evaporation of tungsten of filament takes place. In the halogen lamp, the evaporated tungsten of filament combines with the halogen gas and deposited back on the filament. This process is known as halogen cycle. The halogen cycle increases the life of the lamp and maintains the proper light emission and transmission.
Advantages of Halogen Lamp
The advantages of using halogen lamps include the following −
Halogen lamps come in miniature size.
They can be either single ended lamps or double ended lamps.
In halogen lamps, there is no blackening of the lamp.
Halogen lamps have better color radiation.
Halogen lamps have long life span around 2000 hours.
The lamp efficiency is relatively higher for the halogen lamps, around 22 to 33 lumens/watt.
Halogen lamps have high operating temperature.
Applications of Halogen Lamp
Halogen lamps are used in the following applications −
Public halls lighting
For lighting in factories
Used as projection lamps
Used as headlamps in vehicles
Used for lighting in large gardens
Airport runways lighting
Used as inspection lights and microscope illuminators, etc.
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