First things first: Bioluminescence is the production of light by living organisms, the light emitted by organisms such as glow-worms, deep-sea fish, fireflies and others.
And now some words from Darwinian fantasy storytellers ( from a mainstream article, published December 2020):
We argue that bioluminescence, a complex trait that evolved dozens of times through either novel mechanisms or conserved toolkits, is particularly well suited for these studies. We present an updated estimate of at least 94 independent origins of bioluminescence across the tree of life, which we calculated by reviewing and summarizing all estimates of independent origins.
We focus on luminous organisms that use the shared luciferin substrates coelenterazine or vargulin to produce light because these organisms convergently (repeatedly) evolved bioluminescent proteins that use the same luciferins to produce bioluminescence.