Bioluminescence

Bioluminescence is a special type of illumination created by most life forms in Subnautica. However, not all of them can generate light bright enough to actually help the player with night time navigation, save for the Grue Clusters.

Trivia

 * Bioluminescence is used by many real-life animals for counter-illumination, luring prey, attracting mates, confusing predators, mimicking other animals, communication, and as a warning to would-be predators.