Final answer:
Luciferin produces light when it reacts with the enzyme luciferase, a process known as bioluminescence, which is distinctly different from fluorescence where excitation is from sources like ultraviolet light.
Step-by-step explanation:
Luciferin produces light in organisms when it reacts with an enzyme called luciferase. This biochemical reaction is a form of bioluminescence, which is seen in a variety of organisms, including fireflies and dinoflagellates. While the luciferase enzymes and luciferin substrates may differ among species, the underlying mechanism of bioluminescence is similar—luciferase catalyzes the oxidation of luciferin, resulting in the emission of light. This process is distinct from fluorescence, where light emission is induced by excitation from sources such as ultraviolet light and doesn't involve a chemical reaction between a substrate and an enzyme.