Incandescence

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For the science fiction novel with the same name, see Incandescence (novel)

Molten glassy material glows orange with incandescence in a vitrification experiment.

The incandescent metal embers of the spark used to light this Bunsen burner emit light ranging in color from white to orange to red or to blue. This change correlates with their temperature as they cool in the air. The flame itself is not incandescent, as its blue color is due to various other atomic and molecular energy transitions. The blue color comes from the quantized transitions that result from the oxidation of CH radicals.

Incandescence is the emission of light (visible electromagnetic radiation) from a hot body due to its temperature.^[1] The term derives from the verb incandesce, to glow white.^[2]

In practice, most bodies start to glow visibly in the dark around 400°C (about 670K). Their incandescence is not strictly zero below that temperature, but it is too weak in the visible spectrum to be visible.

The incandescence of a theoretically perfectly black object is known as black body radiation, which is described by relatively simple mathematical equations. For a black body, the distribution of energy emissions across the electromagnetic spectrum is described by Planck's law. The total power emitted by radiation from a black body is given by the Stefan–Boltzmann law. Wien's displacement law predicts the wavelength of peak emission.

Incandescence occurs in incandescent light bulbs, because the filament resists the flow of electrons. This resistance heats the filament to a temperature where part of the radiation falls in the visible spectrum. The majority of radiation, however, is emitted in the invisible infrared part of the spectrum, which is why incandescent light bulbs are inefficient.^[3]

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. While higher temperatures can increase efficiency, there are currently no materials able to withstand such temperatures which would be appropriate for use in fluorescent lamps.

[edit] See also

• Incandescent light bulb
• List of light sources

[edit] References

1. ^ Dionysius Lardner (1833). Treatise on Heat. Longman, Rees, Orme, Brown, Green & Longman. http://books.google.com/books?id=jjYIAAAAIAAJ&pg=PA341&dq=incandescence+becomes-luminous&lr=&as_brr=1&ei=Hyk7SMu8FJHUsgOf28XBCw. "The state in which a heated body, naturally incapable of emitting light, becomes luminous, is called a state of incandescence." 
2. ^ John E. Bowman (1856). An Introduction to Practical Chemistry, Including Analysis (Second American ed.). Philadelphia: Blanchard and Lea. http://books.google.com/books?id=ffTcf4FGOx4C&pg=PA283&dq=incandesce+date:0-1860&lr=&as_brr=1&ei=vy07SMLWOYvAsgP3vPHPDA. 
3. ^ William Elgin Wickenden (1910). Illumination and Photometry. McGraw-Hill. http://books.google.com/books?id=gVZDAAAAIAAJ&pg=PA3&dq=incandescent+low-efficiency+blackbody&lr=&as_brr=1&ei=idBGSJ-RMJGosgPKq42wDQ. 

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