LEDs with Firefly-Inspired Surfaces
Penn State researchers are suggesting that firefly-like structures could improve the efficiency of LEDs. Fireflies and LEDs both have similar obstacles in having produced light reflecting backwards and getting lost. By texturing the surface with microstructures — microscopic projections — more light is able to escape. In most LEDs these projections are symmetrical, with identical slopes on each side. Fireflies’ lanterns also have these microstructures, but the researchers noticed that the microstructures on firefly lanterns were asymmetric. The sides slanted at different angles, giving a lopsided appearance.
Using asymmetrical pyramids to create microstructured surfaces, the team found that they could improve light extraction efficiency to around 90 percent. The asymmetrical microstructures increase light extraction in two ways. First, the greater surface area of the asymmetric pyramids allows greater interaction of light with the surface, so that less light is trapped. Second, when light hits the two different slopes of the asymmetric pyramids there is a greater randomization effect of the reflections and light is given a second chance to escape.
In conventional LEDs, the production process usually produces symmetrical pyramids because of the orientation of the sapphire crystals. The team discovered that if they cut the block of sapphire at a tilted angle, the same process would create the lopsided pyramids. By altering just one part of the production process, they believe their approach could easily be applied to commercial manufacture of LEDs. The researchers have filed for a patent on this research.
source: penn state