Recently something unusual happened: I had an idea that was illustrated and published in Wired. They have a gallery of hybrid animals up, including drawings made by students in the CSU Monterey Bay Science Illustration Program, and my contribution was bioluminescent starlings. I personally think that watching a murmuration of glowing starlings flocking would be amazing. But how does bioluminescence work exactly?
Bioluminescence is light emission from a living creature. How does that happen? Remember that light is a form of energy, and if a particle undergoes a transition from one energy level to another, the difference in energy has to go somewhere and may be emitted as light. Much of the light we get from the sun comes from atomic energy level transitions that happen inside it. But the same thing can also occur in more complex chemical reactions: excess energy can be used to create a new compound, or heat up the reactants, but it may also be emitted as light. (Whether or not this happens depends on the mechanism of the chemical reactions and, as usual, on energy minimization.)
So bioluminescence occurs when a chemical reaction happens, inside a living organism, that emits light. It’s actually relatively common in deep-sea creatures, who don’t have much other light around. But it’s also seen closer to shore in bioluminescent algae, and on dry land with fireflies. What these creatures have in common is that they produce luciferin, a class of pigments that can be oxidized to produce light, and luciferase, an enzyme that catalyzes the reaction. These creatures can then use the bioluminescence to communicate with other creatures, for camouflage, luring prey, or attracting mates.
Some plants show bioluminescence too, though there are many competing theories on whether they gain some evolutionary advantage from it or not. But there are also many researchers working to introduce bioluminescence into plants and animals, by adding the genes that create luciferin and luciferase, or by adjusting their expression. Self-lighting could help with imaging, but making more things bioluminescent has both a practical and an aesthetic appeal.