While we often think we are clever designers, living things often meet or beat the best human designs. It is easy to forget that nature even has living lightbulbs, among them the firefly. Researchers from Penn State decided to compare how fireflies create light and found that they deal with a problem similar to LEDs. The insight may lead to an increase in efficiency for LEDs, which is currently about 50%.
The problem is that some light generated never gets out of the LED (or the firefly’s body). Some light inevitably reflects back into the device. One known mitigation for this is creating a tiny texture pattern on the LED surface which allows more light to escape. These are typically a V-shaped structure etched into the surface. This isn’t news to the firefly, however, which has similar structures on their lanterns as do some other light-generating animals (apparently glowing cockroaches are a thing). However, the organic structures differ from LED textures in an important way.
The firefly’s textured V’s are not symmetrical, instead they are lopsided with one leg of the V sloping at a different angle. Researchers think this allows both an increased surface area and increase in random angles of reflections which gives photons a second chance to escape.
Verified both with computer models and a nanoscale 3D printed prototype, the researchers found that they could produce LEDs with light extraction efficiencies of around 90%. When it comes to getting more light out of an LED, there are two factors: the quantum efficiency and the light extraction efficiency. The first factor measures how many electrons are converted into light and is already near its theoretical limit in modern devices. The other factor is the light extraction efficiency, which is what this work improves. The team has found that changing how crystalline sapphire is cut in the conventional LED manufacturing process can create the lopsided structures, so it is likely that this advance will be coming to an LED near you very soon.
Of course, even the worst LED tends to be a lot more efficient than an old incandescent bulb. Even though white LEDs have become inexpensive and common, there’s a lot more going on in them then you might think.