Technical
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Incandescent Lamps

The principal types of incandescent lamps are general-purpose, special-purpose, decorative and reflective. The luminous efficacy of incandescent lamps in the 25 to 1000W range is between approximately 9 and 19 lm/W for lamps with an average life of 1000 hours.

Incandescent lamps are classic thermal radiators in which electricity flows through a tungsten wire in an enclosed glass bulb filled with a vacuum or inert gas, heating it to approximately 2600 to 3000K and making it glow. Most of the radiation emitted is at the infra-red end of the spectrum.

The main properties of an incandescent lamp – namely its luminous efficacy and life – are influenced largely by filament temperature. The higher the filament temperature, the higher the luminous efficacy but the shorter the lamp life.

A reduction in lamp life is a consequence of the rapid increase in the rate of vaporization of the tungsten atoms as the temperature rises. This process produces a black coating on the bulb, and ultimately causes the filament to break. Blackening of the bulb can be effectively countered by using as heavy an inert gas as possible (argon, krypton or xenon) and ensuring that this gas is at high pressure to reduce the rate at which the tungsten vaporizes.