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. Note that the flame itself is not incandescent as its blue color is due to various other atomic and molecular energy transitions.
Incandescence is the release of electromagnetic radiation, usually visible radiation, from a body due to its temperature. Black body radiation is the incandescence of a theoretically perfectly black object, 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.
At temperatures commonly occurring on Earth (about 100K - 2000K), the release of radiation is predominantly in the infrared and visible regions of the electromagnetic spectrum.
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.
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