Incandescence

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Incandescence is the release of electromagnetic radiation, usually visible radiation, from a body due to its temperature. The distribution of energy emissions across the electromagnetic spectrum is described by Planck's law; at temperatures occurring on Earth (say 100-2000K), the release of radiation is usually predominantly in the infrared and visible regions of the electromagnetic spectrum. The total power emitted by radiation is given by the Stefan-Boltzmann law.

Incandescence occurs in light bulbs, because the filament resists the flow of electrons. This resistance heats the filament to a temperature where part of the black body radiation falls in the visible spectrum. The majority of radiation, however, is emitted in the invisible infrared and lower frequency spectra, which is why incandescent light bulbs are very inefficient.

Fluorescent lamps do not function by means of incandescence, rather by a combination of thermionic emission and atomic excitation due to collision with high energy electrons. In an incandescent lamp, only the electrons at the top of the band can participate. Higher temperature can increase efficiency but we do not have materials that can withstand much higher temperature.

See also

• Incandescent light bulb
• Black body
• List of light sources