Halogen light bulbs are incandescent lamps containing a halogen gas instead of an inert gas in the bulb. Halogen bulbs are more efficient, give higher quality lighting and have a longer rated life compared to ordinary incandescent bulbs.
In an ordinary incandescent lamp, evaporation of the tungsten filament happens unevenly over time, leading to darkening of the bulb and its eventual burnout. However, in a halogen light bulb, the halogen gas chemically deposits the evaporated metal back onto the lamp filament, thereby extending the life of the lamp. While the price of halogen lamps is typically higher than that of ordinary incandescent bulbs, halogen light bulbs are more energy-efficient which makes them more economical to run.