There is a special type of incandescent bulb called halogen bulb. Incandescent bulbs glow as electricity passes through the thin tungsten filament. This filament is surrounded by a neutral gas made of nitrogen or an inert argon gas, which is encased in a glass bulb. The advantage of halogen lamps to ordinary incandescent lamps comes from the design of the former. Halogen bulbs have smaller encasement and the tungsten filament in the bulb is made of a halogen gas which can be either iodine or bromine. As the current passes through the tungsten wire, it glows hot and some of the atoms escape out of the filament. These tungsten vapor atoms collide with halogen gas atoms. Tungsten atoms are then re-deposited onto the filament. This process inside a halogen bulb is called the halogen cycle. This is why the filament lasts longer before burning out than the filaments of incandescent bulbs. The glass envelope is also made of quartz which withstands extremely high temperatures at which ordinary glass might burst. Halogen lamps give a characteristic crisp and white light that is brighter than any typical incandescent lamps.
The presence of the halogen inside the bulb encasement allows reversible chemical reaction with tungsten atoms. When electric current flows through the filament, it glows hot. The extremely high temperature causes some of the tungsten to vaporize into atoms. In typical incandescent bulbs, just like the ones in your table lamps, tungsten atoms gradually condense onto the inner surface of the glass bulb. This slowly leads to blackening of the bulb as well as loss of some efficiency in lighting. As this process progresses, the filament thins until it burns out and the bulb gets busted.
The rapid loss of tungsten through vaporization and deposition onto the inner glass surface is, however, delayed by halogen lamps. Incandescent bulbs use inert gas which does not chemically combine with tungsten atoms, thus, deposition of the metallic element onto the glass is not halted. A particular advantage of inert gases like argon, neon or nitrogen in these bulbs is that they do not react with hot tungsten to produce a run away chemical reaction. This has been understood by chemists and physicists centuries ago since the inception of light bulbs. If it were oxygen they used, then bulbs would not last more than a few seconds as it would rapidly oxidize hot tungsten and you would get a blackened and busted bulb in seconds.
The manufacture of halogen lamps depends on the voltage design of the bulb which in turn affects the rate of tungsten evaporation. So as voltage increases, the rate of vaporization also increases. The higher the rate of vaporization, the more halogen gas the bulb must contain. Therefore, the amount of halogen gas also depends on the voltage. Temperature also has an influence on the life span and performance of the bulbs. Halogen lamps require higher temperature so that sufficient chemical combination between the gas and tungsten atoms can occur. Manufacturers make sure that the amount of halogen is in proportion to the operating voltage of the lamp. If the voltage is too high for the amount of halogen, tungsten vaporization overwhelms the halogen cycle and the lamp darkens. If there is too much halogen, the lamp may not function properly.
Safety handling of these lamps should also be observed. Halogen lamps have glass surfaces that are closer to the filament. Thus, they are smaller but hotter than incandescent bulbs, as they should achieve the right temperature requirement for halogen cycle to be possible. Touching the bulb while it is turned on is seriously discouraged. A halogen lamp may also cause fire if situated near flammable materials. In addition, halogen bulbs are high-energy emitters and release ultraviolet radiation. Thus, it may be possible to sustain UV damage upon a certain amount of exposure. However, there are lamps whose glass surfaces have UV filter coating.
Author Resource:-
Jo is a content writer for 'Litelec' (http://www.litelec.co.uk), a UK company that specializes in the distribution of electric light bulbs, light fittings, electrical accessories and related merchandise for household and business purposes which they market at especially competitive prices. If you wish to lower your electricity costs and at the same time contribute to the safety of the ecosystem then begin by using halogen light bulbs at home and if you have further cheap light bulbs requirement then check out Litelec.
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