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Bioluminescence refers to the creation and emission of light by a living organism. It is a type of chemiluminescence: the emission of light because of a chemical reaction. Organisms use bioluminescence and light up certain parts of their bodies for various reasons. For many underwater organisms, bioluminescence is helpful for attracting prey, in the form of a light lure dangling in front of a fish’s mouth or a glowing liquid squirted out by a squid. The organism we might immediately identify as using bioluminescence is one that lights up in the air: the firefly.


Fireflies use a chemical reaction to produce and emit light, exhibiting bioluminescence. This chemical reaction involves the combination of oxygen, calcium, a type of energy called adenosine triphosphate (ATP), and a chemical called luciferin. If this combination happens near a bioluminescent enzyme called luciferase, light is produced and the firefly’s abdomen begins to glow. The reaction itself happens in the firefly’s light organ: the organ lights up when oxygen is available, and goes dark when it is not available. Therefore, the firefly is able to selectively add oxygen to the other chemicals, choosing when to begin the chemical reaction and produce its light. The firefly can also move oxygen from outside its body to its inner cells using smaller tubes called tracheoles.


One interesting feature about fireflies’ bioluminescent light is that it is cold light. Cold light refers to a specific type of light that occurs without the production of much heat. In most chemical reactions, energy is given off as heat – but in bioluminescence, this is not the case, so very little energy is lost during the chemical reaction. The production of cold light instead of hot light allows fireflies to glow without burning up.


Bioluminescence is utilized by many organisms – from fireflies to countless deep-sea creatures – potentially making it the most common form of communication on the planet. Firefly larvae can use it as a warning mechanism to ward off predators, and adult fireflies can glow to identify members of their species or of the opposite sex as part of mating rituals. Whatever the purpose, bioluminescence remains a unique and exciting scientific phenomenon that continues to light up our world.