Physical Science - Other

Halogen Light Bulb Thoery



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Halogen light bulbs work in the same manner as our old friend the incandescent light bulb. You know, the one invented by Thomas Edison.

Halogen and incandescent light bulbs operate by heating a filament, most commonly made of tungsten, today, until it glows. The glowing filament is what creates the light, but it also creates a lot of heat. In fact, the energy that a standard incandescent light bulb uses creates almost 10 times as much heat as it does light.

To keep the filament from burning up an incandescent light bulb is filled with a relatively inert gas like nitrogen or argon. Since the gas inside the light bulb doesn't react with the tungsten, even at a high temperature, the filament doesn't burn. However, the tungsten from the filament does evaporate. Over time the envelope, or the glass enclosure of the bulb, darkens with deposited tungsten, and the filament thins until the bulb burns out. This happens by the time the lamp has been used no more than 2000 hours on average.

This is where a halogen light bulb deviates from an incandescent one. A halogen bulb is filled with a highly reactive element from the halogen group on the periodic table. This element could be fluorine, chlorine, iodine or bromine. These elements react with the tungsten as it evaporates. When the halogen compound of tungsten touches the filament the extremely high temperature of the tungsten filament causes the halogen and the tungsten to separate replacing the tungsten from where it had evaporated and returning the halogen gas into the bulb to continue the cycle. This cycle helps the filament to stay intact and prevents the tungsten from depositing on the envelope. Because of this halogen bulbs tend to last a lot longer than incandescent bulbs.

Another advantage of the operation of the halogen bulb is that it can be run at a higher temperature. If you were to run a standard incandescent bulb at the temperatures that halogen lights operate the filament would evaporate very quickly but in the halogen bulb, since the tungsten is continually returned to the filament when it evaporates that is not a concern. These higher temperatures increase the efficiency of the halogen light to as much as double the efficiency of the standard incandescent bulb.

While not as efficient as fluorescent lighting, halogen lighting is more efficient than traditional incandescent lighting. Since fluorescents and compact fluorescents don't work well in all situations, you could see some energy savings from halogens.

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