Incandescent lamps
Incandescent lamps are classic thermal radiators in which electricity flows through a tungsten wire in an enclosed glass bulb filled with an inert gas or completely evacuated. The wire heats up to approximately 2600 to 3000 K making it glow white hot. Most of the radiation emitted is at the infra-red end of the spectrum.
Relative spectral power distribution of incandescent lamps
The main properties of an incandescent lamp, namely its luminous efficacy and life, are influenced largely by the filament temperature.
Operating characteristics of incandescent lamps
The higher the filament temperature the higher the luminous flux and efficacy but the shorter the lamp life.
A reduction in lamp life is a consequence of the rapid increase in the rate of evaporation of the tungsten filament as the temperature rises; this process not only produces a black coating on the bulb but also ultimately causes the filament to fail.
Blackening of the bulb can be effectively countered by having a dense 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 filament evaporates.
The principal types of incandescent lamp are general purpose lamps, special purpose lamps, decorative lamps and incandescent reflector lamps. The luminous efficacy of incandescent lamps in the 25W to 1000W range is between about 9 and 19lm/W for lamps with an average life of 1000 h.
Incandescent lamps are classic thermal radiators in which electricity flows through a tungsten wire in an enclosed glass bulb filled with an inert gas or completely evacuated. The wire heats up to approximately 2600 to 3000 K making it glow white hot. Most of the radiation emitted is at the infra-red end of the spectrum.
Relative spectral power distribution of incandescent lamps
The main properties of an incandescent lamp, namely its luminous efficacy and life, are influenced largely by the filament temperature.
Operating characteristics of incandescent lamps
The higher the filament temperature the higher the luminous flux and efficacy but the shorter the lamp life.
A reduction in lamp life is a consequence of the rapid increase in the rate of evaporation of the tungsten filament as the temperature rises; this process not only produces a black coating on the bulb but also ultimately causes the filament to fail.
Blackening of the bulb can be effectively countered by having a dense 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 filament evaporates.
The principal types of incandescent lamp are general purpose lamps, special purpose lamps, decorative lamps and incandescent reflector lamps. The luminous efficacy of incandescent lamps in the 25W to 1000W range is between about 9 and 19lm/W for lamps with an average life of 1000 h.