The emission of light without heat by living organisms

It occurs in glow-worms and fireflies, bacteria and fungi, and in many deep-sea fish; in animals it may serve as a means of protection (e.g. by disguising the shape of a fish) or species recognition or it may provide mating signals.

The light is produced during the oxidation of a compound called luciferin, the reaction being catalysed by an enzyme, luciferase.

It may be continuous (e.g. in bacteria) or intermittent (e.g. in fireflies)