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What is a halogen lamp ?

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Halogen lamp is the latest member in the family of incandescent lamp possessing numerous advantages over the ordinary incandescent lamp. Halogens area group consisting of the elements fluorine, chlorine, bromine and iodine. The life and efficiency of an ordinary incandescent lamp are affected by the gradual evaporation of tungsten and also its operating temperature. The addition of a small amount of any halogen vapour to the argon gas filing of a lamp has the effect that under certain conditions the metal evaporated from the tungsten filament on reaching the relatively low temperature near the wall of the envelope forms a compound of tungsten halogen and being very voltage tungsten halogen suffers from thermal diffusion in the direction of filament and on reaching the filament at high temperature it decomposes into the tungsten and halogen. In this way the evaporated tungsten is returned back and restored to the filament by means of a chemical reaction. Halogen therefore works as a transport gas. This regenerative cycle maintains the interior of the bulb in a clean condition without depositing any metal vapor on the wall. The action requires a higher bulb temperature of about 250℃ that can be withstood by the glass. Therefore a relatively expensive material quality is chosen as the envelope material and its size is kept very small in which high gas filling pressure in made possible. This gives long life of about 2000 hours to the lamp with higher light output of about 22-23 lumens/watt.

Halogen lamps are made in the standard wattage of 300 W, 500 W, 600 W, 1000 W, 1500 W & 2000 W but sometimes these are made upto 5 kW. These lamps are suitable for outdoor illumination of buildings, sports grounds, parks, air ports, fountains etc. and also used in public halls, sports halls, factories, photo film, T.V. studios, overhead projectors, car lighting, signaling etc.

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