<P> There are several different shapes of filament used in lamps, with differing characteristics . Manufacturers designate the types with codes such as C - 6, CC - 6, C - 2V, CC - 2V, C - 8, CC - 88, C - 2F, CC - 2F, C - Bar, C - Bar - 6, C - 8I, C - 2R, CC - 2R, and Axial . </P> <P> Electrical filaments are also used in hot cathodes of fluorescent lamps and vacuum tubes as a source of electrons or in vacuum tubes to heat an electron - emitting electrode . </P> <P> One of the problems of the standard electric light bulb is filament notching due to evaporation of the filament . Small variations in resistivity along the filament cause "hot spots" to form at points of higher resistivity; a variation of diameter of only 1% will cause a 25% reduction in service life . These hot spots evaporate faster than the rest of the filament, which increases the resistance at that point--this creates a positive feedback that ends in the familiar tiny gap in an otherwise healthy - looking filament . Irving Langmuir found that an inert gas, instead of vacuum, would retard evaporation . General service incandescent light bulbs over about 25 watts in rating are now filled with a mixture of mostly argon and some nitrogen, or sometimes krypton . Lamps operated on direct current develop random stairstep irregularities on the filament surface which may cut lifespan in half compared to AC operation; different alloys of tungsten and rhenium can be used to counteract the effect . </P> <P> Since a filament breaking in a gas - filled bulb can form an electric arc, which may spread between the terminals and draw very heavy current, intentionally thin lead - in wires or more elaborate protection devices are therefore often used as fuses built into the light bulb . More nitrogen is used in higher - voltage lamps to reduce the possibility of arcing . </P>

How much heat does a 60 watt incandescent light bulb produce