The term "luciferin" refers to a substance that produces light, usually found in living organisms, such as fireflies or certain bacteria. Full definition
Despite their name, fireflies are actually beetles which use an enzymatic reaction involving a chemical compound called luciferin to produce their typical greenish flashing light. (newscientist.com)
In his logs Snaith often wanders outrageously off the mark to discuss such things as hairdos at Bennington College, the Roman mile, the Papal Line of Demarcation, the uncommon anatomy of the common raccoon, the use of luciferin in chemiluminescence and the effect of private habits on mores in the reigns of Louis XIV and Louis XV. (si.com)
Fluorescence of Cypridina oxyluciferin is greatly enhanced when it is bound to luciferase; the spectrum is thereby shifted, so that it corresponds precisely to the emission spectrum characteristic of the bioluminescentoxidation of luciferin. (science.sciencemag.org)