Bioluminescent

Bioluminescent refers to organisms or tissues that can produce light through a biochemical reaction occurring within living cells. In most cases, light is generated when a substrate, called luciferin, is oxidized by an enzyme, luciferase, releasing photons. Some organisms use photoproteins that emit light when triggered by calcium ions. Bioluminescence is distinct from fluorescence, which relies on external light to excite a pigment.

The chemistry of bioluminescence varies among groups. The classic luciferin–luciferase systems include many marine organisms and fungi, as well as certain insects such as fireflies, where the reaction often requires ATP and oxygen to emit light. Other organisms rely on photoproteins, such as aequorin in jellyfish, which emit blue light in response to rising calcium levels; in some species this light can be transferred to other pigments to produce different colors. Symbiotic relationships also exist, with luminescent bacteria living in specialized organs of marine hosts and providing light for signaling or counter-illumination.

Bioluminescence is particularly common in the ocean, especially in deep or dimly lit habitats, where light production aids in communication, predation, camouflage, or deterrence. Terrestrial examples include fireflies, which use light signals for mating, and certain luminous fungi. In marine systems, light organs and glow-producing bacteria enable behaviors such as lure creation by anglerfishes or counter-illumination by small squid and shrimp.

The study of bioluminescence has influenced biology and biotechnology, leading to applications in imaging, biosensing, and environmental monitoring. The color and duration of emitted light vary by organism and ecological role.