Bioluminescence is light emitted by living organisms. Yellow-green light is produced by various insects including glow-worms and fireflies, but it is in the oceans where we see most animal lights.
The light is produced in a chemical reaction in which an enzyme, luciferase, stimulates a reaction between molecules called luciferins and oxygen, which results in the emission of light as well as oxyluciferin. It is in effect a cold-light source. Some use their own luciferins to produce light, either from many small sites or in special light organs with reflectors, lenses and even colour filters.
In some of the deep-sea anglerfishes the light is produced by bacteria living within special bulbous light organs. Marine bioluminescence is usually blue or green but there are variations, and a few predatory fishes have the ability both to transmit and to see red light, providing them with a private visual system for detecting prey. Light organs on the undersides of fishes and squids camouflage their owners against down-welling light from the surface, but some organisms’ fl ashing displays and spark-like luminous discharges are designed to confuse predators.
Oliver Crimmen, senior fish curator, Natural History Museum