Incandescence

Incandescence is the emission of light from a material as a result of its high temperature. The light is generated by thermal radiation from the hot body, rather than by electronic transitions or chemical reactions. In everyday language, a substance glows when it is incandescent. The term is often contrasted with luminescence, which includes fluorescence, phosphorescence, and chemiluminescence.

Etymology: the word derives from Latin incandescere, meaning to glow white, and entered English through the adjective incandescent. In practice, incandescent light appears as the material reaches temperatures sufficient to produce visible wavelengths of electromagnetic radiation. Metals first glow dull red, then bright red, orange, yellow, and ultimately white-hot as temperature rises. The exact color depends on the emissivity and spectral properties of the material.

Physics: Incandescence is explained by blackbody radiation. Planck's law describes the spectral distribution of emitted radiation from an idealized blackbody at a given temperature; the total power emitted increases with temperature according to the Stefan-Boltzmann law, and Wien's displacement law shows the peak wavelength shifting to shorter values as temperature rises. Incandescent sources emit a broad spectrum with a substantial infrared component, making them relatively inefficient for producing visible light.

Applications and examples: The most familiar incandescent source is the filament in traditional lightbulbs; heated components in metalworking are another practical instance. In astronomy, stars are incandescent bodies whose light arises from thermal radiation. Fires and hot metals are everyday examples. Modern lighting often favors non-incandescent technologies due to higher luminous efficacy and lower heat output.