From natural sunlight to bulbs that glow and lasers that produce narrow beams, we use light to explore our world, to communicate, for security, and even as a weapon. But turn down the brightness and you can find a range of creatures that create their own light for similar purposes. Aided by advances in the sensitivity of color cameras, in Light on Earth, the venerable Sir David Attenborough takes viewers on an international exploration of bioluminescence in some of the darkest places on the planet.
We are shown how flashes from fireflies are used to attract mates and how they also serve to seduce prey or to steal it from spiders. A species of millipede found in the mountains of California, whose daytime coloration warns predators to stay away from its cyanide-containing body, uses bioluminescence to give the same warning at night. For some small or immobile underwater animals, bioluminescence is triggered by the attack of a predator; the intense glow turns the predator into potential prey as it is suddenly illuminated in the murky dark.
We see the motion of dolphins evoke a blue glow caused by bioluminescent dinoflagellates in the surrounding water, and gnat larvae turn the roof of a cave into a starlit sky to trick their prey. These observations hint at just how much more might be seen in the dark by animals that produce their own light. For scientists, however, seeing the light is only the first step. The biggest challenge may come from trying to understand why many of these creatures produce light in the first place.