In this article we will discuss about:- 1. Introduction on Halogen Lamp 2. Principle of Operation of Halogen Lamp 3. Safety 4. Handling Precautions.
Introduction on Halogen Lamp:
A halogen lamp (also called tungsten-halogen lamp or quartz halogen lamp) is an incandescent lamp wherein a tungsten filament is sealed into a small transparent envelope filled with a halogen gas such as iodine or bromine added to the inert gas of the bulb.
This causes the evaporated tungsten to resettle and blackening of the lamp is eliminated. The halogen lamp can operate its filament at a higher temperature than in a standard vacuum or inert-gas filled lamp, without loss of operating life. This gives it a slightly higher efficiency (10 – 20 %) than standard incandescent lamps. It gives a bright yellow light which is considered to the nearest to daylight from any lamp.
Principle of Operation of Halogen Lamp:
In an ordinary incandescent lamp, the thickness of the filament may vary slightly. Although the resistance of the filament is higher at the thinner position, the current is same. Therefore the thin areas are hotter than the thicker parts of the filament. The rate of tungsten evaporation will be higher at these points due to increased temperature, causing the thin areas to become even thinner, creating runway effect until the filament fails.
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The halogen lamp runs at higher temperature which would cause unacceptably short lamp lifetimes in ordinary incandescent lamps, allowing for higher luminous efficiency, apparent brightness. The lamp during operation is very hot to prevent compensation at the glass surface. The halogen lamps envelope must be made of hard glass or fused quartz, instead of ordinary soft glass.
A further development that has been added to halogen lamp efficiency is an infrared refracture coating (IRC). In this type of lamp the quartz envelope is coated with dichroic coating which allows visible light to be emitted while reflecting a portion of the infrared radiation back on to the filament will create a hot spot on the bulb surface when the bulb is turned on. This heat causes the leakage of gas and may lead to failure or explosion and creating a serious safety hazard. Therefore quartz lamps should be handled either by using clean paper towel or carefully holding the Porcelain base.
A typical halogen lamp is design to run about 2000 hours twice as long as a typical incandescent lamp uses:
1. Quartz halogen lamps are used in scientific, medical and dental instruments.
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2. Halogen lamps are suitable for illumination of sports grounds, parks, factories and airports etc.
Safety while Using Halogen Lamps:
Because of halogen lamp operates at very high temperatures, it, can pose fire and burn hazards.
General-purpose lamps usually have a UV absorbing glass filter over the bulb. Alternatively, lamp bulbs may be coated to filter out UV radiation when this is done correctly a halogen lamp with UV inhibitors will produce less UV than its standard incandescent counterpart.
Handling Precautions for Halogen Lamps:
Any surface contamination, notably fingerprints can damage the quartz envelope when it is heated-Contaminations such lamps are called halogen- infrared lamps, and they require less power than standard halogen lamps to produce any given light output the efficiency increase can be as much as 40% when compared to its standard equivalent. A halogen incandescent lamp has a height spectrum.