Bioluminescence — living light — is widespread in the oceans of the world. In the deep sea, where sunlight is absent, more than 90% of the animals are luminescent. Bioluminescence serves a number of important functions, including prey attraction, illumination of prey, mate attraction, and predator avoidance. Light emission is produced as a result of the oxidation of a substrate molecule, luciferin, in a reaction catalyzed by a protein, luciferase. There are dozens of unique biochemical families of luciferins and luciferases, but only a handful have been characterized.