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It will never be totally dark on Earth—not as long as the planet is inhabited by certain insects, fish, mollusks, fungi, and worms that produce bioluminescence, or “living light.” It’s the result of internal chemical reactions and the main source of light in the deep ocean.

While most of the light we see comes from a heat source (the Sun, for example), bioluminescence is a “cold” light. It produces low energy without significant heat, but it’s been attracting attention for centuries. The Greek philosopher Aristotle mentioned seeing the light of what is now commonly called foxfire. Charles Darwin described the glowing ocean as he sailed aboard the H.M.S. Beagle in the 1830s.

You can find bioluminescent creatures in the air, on the ground, and in the sea, if you look carefully. (continued)

by
Alice
Cary

–background, VEER Steven Puetzer/Photonica/Getty Images; inset, Bev Wigney

HOW IT WORKS

Bioluminescence’s chemical reaction involves three substances that react with oxygen to produce light:

■ a molecule called luciferin

■ an enzyme called luciferase

■ an energy molecule called adenosine triphosphate (ATP), which is found in all living things

For example, fireflies glow when luciferase reacts with luciferin. In the presence of oxygen and ATP, these agents produce a short-lived, high-energy compound that glows.

It’s not currently practical to use bioluminescence for home lighting (the chemicals are expensive and difficult to make, and the light would be very dim). However, the phenomenon is being studied for a wide variety of uses, such as testing water and food quality, genetic engineering, and even land mine detection.