Among the earliest chemical causal hypotheses for the Will-o’-the-wisps is a combustion arising from a mixture of Hydrogen Phosphide (PH3) and Hydrogen Sulfide (H2S) mixtures of which will sometimes burst into flame. In the case of will-o’-the-wisps and as with fireflies, there is no heat to go with the “light”.
This might be called the marsh gas hypothesis. As the wisps are the most frequently observed in wet swampy areas. (source: Mullen-Erzbach, Abh Naturw. Verein Bremen, 14:217, 1897).
Phytoplankton, jellyfish, zooplankton and many species of fish produce marine bioluminescent light. Other than bioluminescence fireflies, I have had but one encounter. It was on a summer evening on the beach at the VCR and as each wave ran up the beach and then ebbed, millions of points of light lit the beach. It was spectacular, awesome, unbelievable, inspiring.
The mechanism was the same as the light of the firefly. Luciferin (a pigment) and luciferase (an enzyme) and as electrons move from one orbit to another, photons of light are emitted. This requires energy. For example, this energy can be delivered by adenosine triphosphate (ATP). With adequate oxygen, Adenosine diphosphate (ADP) is converted to ATP.
In marine waters, breaking waves or boat wakes may stimulate bioluminescent plankton to emit light. 0.440 and 0.479 micron wave length light.
Terrestrial bioluminescent organisms greenish photons with wavelengths of 0.505 microns. Bioluminescent There are some 50 white-spored basidomycetes fungi species that are bioluminescent (wavelengths between 0.520 and 0.530 microns).
An outstanding web site on bioluminescence can be found at: http://www.quantum-immortal.net/physics/biolum.php