concept

Luciferin

The small fuel molecule that is oxidized to produce light in a bioluminescent reaction - the name comes from the Latin *lucifer*, "light-bringer". The enzyme luciferase joins luciferin to oxygen, kicks it into an excited state, and it releases a photon as it drops back down. Strikingly on Earth, there are at least dozens of chemically distinct luciferins, because glow evolved independently dozens of times - each lineage stumbling onto its own fuel.