Bioluminescence
Light made by living things through a chemical reaction, in which an enzyme called luciferase makes luciferin react with oxygen.
Bioluminescence is light produced by a living organism. Fireflies, many deep-sea fish and squid, some fungi, certain plankton and some bacteria all do it. Unlike a glow-in-the-dark sticker, which stores light and releases it later, bioluminescence makes new light from a chemical reaction.
The reaction involves a light-producing molecule, called a luciferin, and an enzyme, a luciferase, which makes it react with oxygen. The reaction leaves a molecule in an excited, high-energy state, and it sheds that extra energy as visible light rather than heat, which is why bioluminescence is often called cold light. Both names were coined by the French physiologist Raphaël Dubois. The chemistry differs between groups, since fireflies, bacteria and marine animals evolved their own versions, but every system studied so far needs oxygen.
In the sea most bioluminescence is blue or blue-green, the colours that travel furthest through water. The luciferase of the sea pansy, a soft coral, on its own gives out blue light peaking at 482 nanometres. Animals use their light to lure prey, startle predators, find mates or hide their silhouettes against the faint light from above.
Glowing bacteria can light up the sea, or even a wound, in huge numbers. Many switch their light on only when enough of them are crowded together, a behaviour called quorum sensing.
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