Incandescence stems from Latin, meaning ‘to glow white’. It describes a special type of thermal radiation, when visible light is emitted from a hot object. Visible incandescence happens once temperature reaches the Draper point – this is when an object or substance is heated to 525˚C and glows red. The colour changes as the temperature is increased, from red, to yellow, white, then blue. Light is produced by hot objects because of the emission of photons from high energy atoms, which get their energy from heat.
Incandescence occurs naturally. Sunlight is a type of incandescent light – the white hot light produced by the sun’s heat. Volcanic eruptions are also an example of natural incandescence – lava is red because of its heat.
This phenomenon can be exploited to produce incandescent lamps, which use a white hot filament. New technologies have been able to induce incandescence using lasers, which can be useful in soot and particle diagnostics.