The bioluminescence is the faculty for certain alive, plant or animal bodies to produce their own light.
The light emitted by bioluminescence is the result of chemical reactions bringing in an enzyme, the luciferase and a substratum, the luciferine.

The combination of these two organic molecules, in the presence of oxygen, form an excited complex which, to return to his state of energy of balance, emits a photon, that is a particle of light.

For Pyrocystis noctiluca the luminescence is caused by the mechanical agitation and serves to betray his predator by bright, predatory flashes who, lit by these flash, is then vulnerable.