Bioluminescence

Bioluminescence was a natural occurrence in many kinds of insects and marine animals, as well as types of alien creatures, that caused them to give off light.

Fireflies and glow worms were bioluminescent. (TV: Thin Ice)

The Star Whale under the Starship UK was bioluminescent. (TV: The Beast Below)

The Mantasphids were bioluminescent and provided light for the humans on Myarr after their "surrender". (TV: The Infinite Quest)

Erato was a mobile, bioluminescent vegetative life-form. (TV: The Creature from the Pit)

Bioluminescence was used in the Galactic Seed Vault to provide light. It reacted to the presence of visitors. (PROSE: The Secret in Vault 13)