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What happens when an excited molecule returns to its ground state during bioluminescence?
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Bioluminescence
Time-lapse image of fireflies in the Catskill Mountains, New York. Firefly light is a cold light, with approximately 100 percent of the energy given off as light and only a minute amount as heat. Only light in the visible spectrum is emitted.
In the process of bioluminescence, a high-energy complex—such as the luciferase-luciferyl-adenylate complex in fireflies—is formed through an enzyme-substrate reaction involving luciferin, luciferase, and molecular oxygen.1
When this complex reaches a high-energy excited state, it loses its excess energy by radiating a photon of visible light. As it releases this radiant energy, the molecule returns to its low-energy ground state. Because this conversion of chemical energy into light is highly efficient, very little heat is produced, which is why the resulting emission is often referred to as cold light.12