Exquisite and Energy-Efficient
By Michael Caduto
Dance of the Fireflies (Photo by Mike Lewinski on Unsplash)
As the month of May matures in the North Country, the growing season accellerates at a dizzying pace. Animals have emerged from their winter surival modes, and have arrived from points south, seemingly spring-loaded and determined to complete their life cycles while the warm weather is upon us.
Fields are alive with anticipation for the flash of the first fireflies to appear, insects whose biochemistry manifests as a kind of magical alchemy. When I was a child we captured fireflies and placed them in large glass jars with holes poked in the lids to create living lanterns. The indigenous peoples of Brazil drill holes in hollow gourds, fill them with fireflies and wear them on the head or tied to the ankles to light the way along darkened paths.
In the natural world, beauty and function are often synonymous. The elegant design that makes a firefly’s living light so productive is now being plumbed to explore new ways of increasing energy efficiency in the sources of light that we rely upon in our daily lives.
Unlike the bright yellow reflection of a raccoon’s eyes, or the green of a bullfrog’s gaze caught in a flashlight beam, bioluminescent plants and animals actually create their own light. Illumination helps them find food, lure their prey or detect enemies lurking nearby. Some lights demonstrate aggression, act as defense signals that warn predators to stay away or serve to confuse an enemy while the prey escapes.
Bioluminescence is created when a substance called luciferin combines with an enzyme, luciferase, and, in a reaction with oxygen, produces a cool light. Some animals grow light-producing bacteria in a special organ. Others create their own radiance in photophores or “light bearers”—organs that contain luminous cells whose light is reflected through a layer of pigment and focused by a lens. Many animals have a kind of living headlight, with a reflector behind the light cells and a clear covering in front. Some animals emit a steady glow while others can brighten and dim their lights. Fireflies actually flash but some of the deep sea fishes blink by closing their beacons with flaps of skin.
Fireflies or lightning bugs—which are really beetles in the family lampyridae—are found in many places throughout the world but are most common in the tropics. The light they produce in an organ under their abdomen creates a unique pattern that tells other fireflies both their sex and species. The color of the light also identifies others of their kind.
There are endless variations on this language of light. Certain female fireflies remain lit and attract males that don’t light up. In some species the males gather and flash together, then the females fly to them. A tiny pacemaker in each firefly’s brain senses the signals of others flashing nearby and responds within a fifth of a second. Some of the Photinus and Photuris fireflies synchronize their flashes, creating a choreographed dance of light.
More than 20 firefly species inhabit New England, with around 8-10 species found in Vermont. If you see a yellow light flashing every three seconds, or so, it is the northern twilight firefly, Photinus marginellus. You’ve likely seen Vermont’s most common firefly, Photuris fairchildi, displaying its light pattern of 3-4 quick flashes, with about 2 ½ seconds in between. As the male flies toward the female, over the course of about 10-20 seconds, they both increase the number of flashes in each sequence until their lights become a constant glow.
Once the female of Photuris versicolor has mated, she changes to mimic the light display of the female from a different species. When an unfortunate male of that different species flies in to mate with her, she devours him—the original femme fatale. Various firefly eggs, larvae and pupae also glow to warn predators that in any stage of life fireflies taste bad and are toxic. Since both the larvae and adults are carnivorous, the light may also be used to attract prey. Glowing firefly larvae and the wingless adult females of the Phengodes fireflies are often called glowworms.
Even as firefly lights transfigure, they are also transforming our constant search for new ways to reduce energy consumption and lower carbon emissions in order to fight climate change. About 95 percent of the energy emitted by fireflies is light, while only 5 percent is lost as heat. In contrast, incandescent lightbulbs lose 90 percent of their energy to heat.
LED or “light-emitting diode” lightbulbs are considerably more energy efficient. The “di” in diode refers to “two”—inside each bulb are two kinds of crystals. When electricity flows into the bulb, its energy causes electrons to become excited in a high-energy crystal. The excited electrons jump off that crystal and into the low-energy crystal. The light is created by the energy that the electrons give off when they make this jump.
LED lightbulbs use 85 percent less electricity than incandescent bulbs. Still, most of the LED’s we use today are only about 50 efficient, which pales in comparison to the efficiency of fireflies. But a new kind of LED lightbulb is being developed by electrical engineers at Penn State University that increases efficiency up to 90% by mimicking the design of a firefly’s light-emitting microstructures. The fascinating science behind the evanescent flashes of fireflies on halcyon early-summer nights is illuminating a new way to decrease the carbon footprint of our lighting.
Do just one thing: Install LED lights throughout your home.