What LED bulbs can learn from fireflies
Mimicking a firefly's ridges on LEDs may boost light for camera phone screens or flashes, car headlights or residential lighting.
Wed, Oct 31, 2012 at 10:42 AM
Fireflies' green-yellow flashes are one of the simplest pleasures of summer. Generations of kids have dreamed of lighting backyards with jars full of them. And someday it may be possible to say you've got a light full of fireflies — or at least a firefly-inspired bulb.
New research has found that LEDs that use firefly-inspired lenses need less energy to shine brighter. Scientists have developed a lens for LEDs that is etched with tiny dots, similar to how a firefly's "lantern" is covered in tiny ridges. The lens allows 98 percent of light to pass through it, which is significantly better than a traditional lens, and an improvement similar to coating a lens with an expensive anti-reflective coating.
Ki-Hun Jeong of the Korea Advanced Institute of Science and Technology and colleagues studied firefly abdomens under a scanning electron microscope. They found the lantern part of the abdomens — where the light is produced — is made of three layers, and bears a striking resemblance to a standard LED bulb.
A standard LED is made of a reflective "cup" and a lens sandwiching the light source. Similarly, a firefly's lantern is made of a reflective layer, a light-emitting layer and a cuticle layer, or exoskeleton, covered in tiny ridges. Compared to the rest of the firefly's exoskeleton, the ridges on the parts of the bug's abdomen where light shone through were much more ordered.
Jeong found that the ridges helped the firefly's particular wavelength of light pass through the firefly's lantern more effectively, so they tried etching similar patterns into plastic. Sure enough, creating a similar pattern of dots on an LED lens allowed more light to pass through.
The technique could be used to boost light for camera phone screens or flashes, car headlights, or even just residential lighting, the researchers say.
The inspiration isn't an exact case of borrowing from Mother Nature, as the manmade LED lens is much more regular and ordered than a firefly's behind. The researchers used nanopillars packed into the shape of a honeycomb, rather than the firefly's long ridges. But just like a real firefly, the patterns seemed to work best when the light had a wavelength of 560 nanometers, or the familiar yellow-green glow of a lightning bug.
That doesn't necessarily mean that we'll all be carrying around firefly-colored lanterns. The nanostructures could be tweaked to boost different wavelengths, Jeong said. "Transmittance is very sensitive to the shape of nanostructures,” he added. “The physical dimension can be more optimized for a specific wavelength of light."
The research appeared in the Oct. 29 issue of Proceedings of the National Academy of Sciences.
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MNN tease photo of firefly: Shutterstock