Is it possible to produce light without heat?

Yes – and many living organisms, such as fireflies, the angler fish and some jellyfish, do precisely that, via luminescence. This involves generating photons with wavelengths mainly in the visible region, rather than in the shorter, infrared region corresponding to heat. Some chemical reactions can do this – for example, phosphorus exposed to the air – and also so-called phosphors, which absorb ultraviolet light and re-emit it as ‘cold’ light.

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