Halogen lamps

Halogen lamps operate in the same way as incandescent lamps and have a similar design. The small quantities of halogens (bromine, chlorine and iodine) or their compounds added to the filler gas almost entirely prevent bulb blackening from the evaporated tungsten (within a particular temperature range) so there is no associated loss in luminous flux during lamp life.
 
By using quartz instead of glass, the bulbs of halogen lamps can be made much smaller and the pressure of the filler gas can be increased which enables the lamp life to be extended.