Genplus

A halogen lamp, also known as a tungsten halogen lamp or quartz iodine lamp, is an incandescent lamp with a small amount of halogen such as iodine or bromine added.  
The combination of the halogen gas and the tungsten filament produces a halogen cycle chemical reaction which redeposits evaporated tungsten back onto the filament, increasing its life and maintaining the clarity of the envelope. Because of this, a halogen lamp can be operated at a higher temperature than a standard gas-filled lamp of similar power and operating life, producing light of a higher luminous efficacy and color temperature. Its small size permits its use in compact optical systems for projectors and illumination.