HALOGEN LIGHTS
A halogen light is very similar in construction and operation to an incandescent light bulb. However, improvements in the design increase the amount of visible light produced and reduce the amount of infrared (nonvisible) light emitted. A halogen lamp uses a tungsten filament just like an incandescent bulb, but it is encased in a much smaller quartz envelope. This small envelope is so close to the filament that ordinary glass would melt. Inside this envelope, a gas from the halogen group, a group of reactive gases found in group 7 on the periodic table, is used to react with the heated tungsten metal. These gases, because of their high reactivity, combine with the tungsten metal vapor and redeposit them on the filament. This process of recycling the filament metal helps the filament last much longer than that in an ordinary incandescent light bulb. It is also possible to get the filament much hotter, producing more light. The proximity of the quartz envelope to the filament is why halogen lights become extremely hot compared with ordinary light bulbs.
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