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Bioluminescence is light produced by a chemical reaction within an organism.

At least two chemicals are required. The one which produces the light is generically called a "luciferin" and the one that drives or catalyzes the reaction is called a "luciferase."

The basic reaction follows the sequence illustrated above:
  • The luciferase catalyzes the oxidation of luciferin
  • Resulting in light and an inactive "oxyluciferin"
  • In most cases, fresh luciferin must be brought into the system, either through the diet or by internal synthesis.

Sometimes the luciferin and catalyzing protein (the equivalent of a luciferase), as well as a co-factor such as oxygen, are bound together to form a single unit called a "photoprotein." This molecule can be triggered to produce light when a particular type of ion is added to the system (frequently calcium).

Bioluminescence is
not the same as "fluorescence" or "phosphorescence". (See Myths for more explanation.) In fluorescence, energy from a source of light is absorbed and reëmitted as another photon. In bioluminescence or chemiluminescence the excitation energy is supplied by a chemical reaction rather than from a source of light.
Here is a simplified view of fluorescence:

The mechanism of fluorescence (not bioluminescence)

  1. An electron (yellow) "orbits" the nucleus (blue), minding its own business.
  2. A source of light of an appropriate wavelength (indicating its energy) strikes ...
  3. ...driving the electron into a higher-energy orbital.
  4. The electron is only stable there for a short time whereupon it...
  5. ...returns to the lower energy level...
  6. ...emitting the energy as a longer wavelength photon.
  7. The electron continues on its way...

Note that due to energy loss while in the excited state, the photon emitted will always be longer wavelength (lower energy) than the exciting photon. See the Myths section for a little more explanation.

Find out more about the molecules that make light.

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