lu·cif·er·in 
(l-sĭfər-ĭn)
(l-sĭfər-ĭn)n.
A chemical substance present in the cells of bioluminescent organisms, such as fireflies, that produces an almost heatless, bluish-green light when oxidized under the catalytic effects of luciferase and ATP.
[Latin lūcifer, light-bringing; see LUCIFER + -IN.]