A tungsten-halogen lamp. In these lamps the filament, a wire made of tungsten one hundredth of a millimetre thick, is enclosed in a small quartz envelope inside the bulb. The quartz envelope contains the vapour of an halogen, such as iodine or bromine, which allows the filament to operate at a much higher temperature than in a conventional tungsten lamp. Therefore tungsten- halogen lamps are characterised by a greater brilliance and also a longer life.