Incandescence

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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]

Contents

Practical

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

In practice, virtually all substances start to glow visibly in the dark around 470°C (about 750K) with a very dull red color, assuming no chemical reaction takes place which emits light as a result of an exothermic reaction.[citation needed] Their incandescence is not strictly zero below that temperature, but it is too weak in the visible spectrum to be perceivable.

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, where a filament is at a temperature where part of the radiation falls in the visible spectrum. The majority of the radiation however, is emitted in the 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.

Figurative use

The word 'incandescent' is also used figuratively to describe a person who is wound up to a sustained white heat of anger about something.[4]

See also

References

  1. ^ Dionysius Lardner (1833). Treatise on Heat. Longman, Rees, Orme, Brown, Green & Longman. http://books.google.com/?id=jjYIAAAAIAAJ&pg=PA341&dq=incandescence+becomes-luminous. "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/?id=ffTcf4FGOx4C&pg=PA283&dq=incandesce+date:0-1860. 
  3. ^ William Elgin Wickenden (1910). Illumination and Photometry. McGraw-Hill. http://books.google.com/?id=gVZDAAAAIAAJ&pg=PA3&dq=incandescent+low-efficiency+blackbody. 
  4. ^ Example 1:'...the stadium positively crackled with the incandescent anger of anguished supporters.' Mark Wilson, 'Rangers 1 Unirea 4', Daily Mail, 21 October 2009 [1]. Example 2: '...there's something very funny about incandescent anger.' Mark Fisher, 'Jerry has a cross to bear', The Scotsman, 5 March 2006 [2].

External links

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