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The luminescence of the sea is caused by certain organisms that are sometimes present in the water in large quantities, often due to similar conditions to those that cause discoloration of seawater by plankton bloom.
The luminescence itself is produced in two ways:

- By the luminescent organisms themselves, such as the (single-cell) Noctiluca, that are around 1 mm in diameter and the Pyrosoma, that are many centimetres long, and
- Indirectly because the luminescent organisms use for the luminescence colonies of luminescent bacteria, that are accumulated at certain points in their body.

It is thought possible that sea waves in a field of these organisms take on a smoother surface as a result of an oily excretion from these organisms.
The luminescence may sometimes take on certain specific forms. For example the name 'milk sea' from the phenomenon where the sea spreads an equal light over a great area, that often contrasts considerably with the darker air above it. Milk sea is apparently only or virtually only observed in certain parts of the Indian Ocean and the Indonesian seas, e.g. east of Cape Guardafui and south of Java. Especially in the months of July, August and September, milk sea is observed there a lot.
Another phenomenon is that where the luminescent phenomenon looks like exploding bubbles or spots rapidly increasing in size. This phenomenon is chiefly limited to the Indian Ocean and especially the Arabian Sea.
A very special form is the 'Phosphorescent wheel' ('luminescent wheel')