Halogen lamps are thermal radiators. Unlike ordinary incandescent lamps, however, they are filled with a gas that contains small amounts of halogens or halogen compounds. Within a certain temperature range, these additives enable volatizing tungsten atoms to be intercepted and thus virtually prevent blackening of the bulb and the consequent decrease in luminous flux.

In the halogen cycle, the tungsten atoms that evaporate from the filament combine with halogen atoms and are re-deposited on the filament. This makes for greater luminous efficacy and a longer lamp life. Owing to the small dimensions of the burner and filament, precise optical control is possible.