Science

Fireflies' "lopsided pyramids" get copied in brighter LEDs

By copying microstructures on fireflies' abdomens, scientists have boosted the light extraction efficiency of LEDs
By copying microstructures on fireflies' abdomens, scientists have boosted the light extraction efficiency of LEDs
View 3 Images
A scanning electron microscope image of the 3D-nanoprinted microstructures
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A scanning electron microscope image of the 3D-nanoprinted microstructures
By copying microstructures on fireflies' abdomens, scientists have boosted the light extraction efficiency of LEDs
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By copying microstructures on fireflies' abdomens, scientists have boosted the light extraction efficiency of LEDs
A comparison of light that emitted from the symmetric and asymmetric structures
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A comparison of light that emitted from the symmetric and asymmetric structures

Although LEDs are far more energy-efficient than incandescent bulbs, most commercial models are reportedly only about 50 percent efficient at emitting the light that they generate. This is known as their light extraction efficiency, and researchers have drastically increased it by copying fireflies.

Many existing LEDs have arrays of pyramid-like microstructures etched onto their surfaces, which help the generated light to be emitted from that surface, as opposed to being reflected back in by it. Fireflies also have such structures on their abdominal "lanterns," which serve the same purpose.

Recently, however, Pennsylvania State University doctoral student Chang-Jiang Chen discovered that unlike the microstructures on the LEDs, those on the insect were asymmetrical. He later found that the same was true of the light-emitting spots on a certain type of cockroach.

With that in mind, Chen and colleagues utilized nanoscale 3D printing technology to create arrays of microscopic lopsided pyramids (pictured below) on the surface of otherwise-conventional LEDs. When tested, those LEDs were found to have a light extraction efficiency of up to 90 percent.

A scanning electron microscope image of the 3D-nanoprinted microstructures
A scanning electron microscope image of the 3D-nanoprinted microstructures

According to the researchers, there are a couple of reasons for this increase. First of all, the asymmetric pyramids have more surface area than their symmetric counterparts, allowing for a greater interaction of light with the surface.

Secondly, when some of the light is reflected back in by the pyramids' two differently-angled slopes, those reflections are of a more random nature – this bounces the light around more, giving it another chance to escape the LED.

A comparison of light that emitted from the symmetric and asymmetric structures
A comparison of light that emitted from the symmetric and asymmetric structures

The scientists are now looking into collaborating with manufacturers to commercialize the microstructure application process, which they say could easily be added to existing LED production facilities.

A paper on the research, which was supervised by Prof. Stuart (Shizhuo) Yin, was recently published in the journal Optik.

Source: Penn State

4 comments
amazed W1
Important as this discovery is, we need in parallel a proper organised investigation as to why certain LED sources used as "lights" produce less "visibility" even though they cause brighter reflections, and so as far as eyes are concerned, brighter images. It might have something to do with lessening the contrast between objects and the background, or the effects of a much smaller image on the retina, as with vehicle headlights. Or it might be much simpler, just that there is an optimum brightness to see anything, that is influenced by both specular and non-specular reflection. It needs practical observations of human responses as well as theoretical analysis
Nik
Great news! Anything that helps me see the light, must be good. More light for the same money, (almost) is always welcome.
Michael Crumpton
This is amazing! A near doubling of efficiency of LEDs means less heat and more light for the same power input. Hopefully this is not too expensive to implement.
Catweazle
Fascinating. You learn something new every day. I wonder how the fireflies and cockroaches managed to work out that using nanoscale asymmetric pyramids on the surface of their photochemical emitters significantly improved the emission efficiency...
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