Bioluminescence

The production of visible light by a living organism through a chemical reaction, most often between a light-emitting molecule called luciferin and an enzyme, luciferase, that catalyzes its oxidation. It has evolved independently many times across very different groups of organisms, on land in fireflies, which use flash patterns to attract mates, and much more widely in the ocean, where the majority of species living below the sunlit surface layer are bioluminescent in some form, from single-celled dinoflagellates that flash when disturbed by a wave or a swimming animal to deep-sea anglerfish that dangle a lit lure to attract prey in total darkness. The reaction is remarkably efficient, converting nearly all of the energy released into light rather than heat, unlike an incandescent bulb.