The emission of light without heat by living organisms. The phenomenon occurs in glow-worms and fireflies, bacteria, fungi, some dinomastigotes, and in many deep-sea fish (among others); 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 composition of which varies according to the species), the reaction being catalysed by an enzyme, luciferase. Bioluminescence may be continuous (e.g. in bacteria) or intermittent (e.g. in fireflies). See also photophore.

https://biolum.eemb.ucsb.edu Comprehensive overview of bioluminescence hosted by the University of California at Santa Barbara