concept

Fluorescence

When a material absorbs light from outside and immediately re-emits it at a different color (usually shifted toward longer wavelengths). Unlike bioluminescence: fluorescence makes no light of its own - cut the incoming light and the fluorescence dies instantly, because it only borrows and reshades existing light. This is a common confusion: a creature that "glows under UV" is fluorescing, while a creature that shines in total darkness is bioluminescent. Some use both: the crystal jelly makes blue light chemically, then lets GFP shift it to green.