Thermal radiator where light is created by heating a Tungsten filament. The incandescent filament is enclosed in a glass bulb filled with an inert gas such as nitrogen which prevents it from oxidising and delays the vaporisation of the filament material. Incandescent lamps are available in numerous forms, the main groups being general service lamps with pear-shaped, clear or frosted bulbs, reflector lamps with a variety of internal reflective coatings and PAR lamps made of moulded glass with integral parabolic reflector.