Halogen lamps are light bulbs which work in a different way from ordinary filament lamps or fluorescent lamps.
In a halogen lamp, there is a tungsten filament which is heated by its resistance to electricity passed through it, but the filament is encased in a small, thick glass bulb, containing some halogen gas: usually Iodine or Bromine.
The filament is produced to heat to a higher temperature than in a normal filament lamp, and atoms of tungsten evaporate, undergoing a reversible reaction with atoms of the gas around them, combining in the heat, and then dissociating as the molecules formed are moved to cooler regions within the gas bulb by convection, the tungsten redepositing on the filament.
This cycling means the filament does not burn out as quickly as in an ordinary bulb, giving them a much longer life - maybe up to 10 years. The higher operating temperature also gives greater efficiency of energy conversion: up to 30% greater than a normal bulb.