Enhanced LED Design Inspired by Fireflies
With the sound of crickets haunting the evening and smell of campfire smoke on their hoodies, my daughters carefully scan the darkness in search of fireflies, or in their world fairies with magic dust.
We never grow bored of these amazing little creatures, which through an oxygen-induced chemical reaction that takes place in their lower abdomen can cause their bellies to light up. The process is called bioluminescence, and it has earned these small flying beetles the nickname “lightning bugs.”
Human observation of fireflies throughout history has led to some useful products, such as emergency glow sticks, which offer the benefit of not needing batteries. But researchers have struggled to achieve the kind of efficiencies studied in fireflies.
One answer to the puzzle, it seems, has nothing to do with chemical reactions. Earlier this month, in two research papers published in the journal Optics Express, scientists from Belgium, Canada and France revealed that the design of a firefly’s abdomen plays an important role in enhancing the bug’s trademark glow.
In fact, they were able to replicate the outside structure of the firefly’s “lanterns” — the organs within the insect’s abdomen — to create a coating that, when applied to the surface of a light-emitting diode (LED), boosted light efficiency by roughly 55 per cent.
It’s a classic example of biomimicry in action. “There are many things in nature that can be adapted for many fields,” said nanotechnology specialist Ali Belarouci, a senior research scientist at the University of Sherbrooke in Quebec. “With the equipment we have today we’re able to see phenomena (in nature) we couldn’t see before.”
Belarouci said Belgian researchers were studying firefly lanterns with an electron microscope when they noticed a pattern of irregular scales with sharp edges and protruding tips. Using computer simulations, they looked at how these scales might affect the transmission of light out of the abdomen.
What was interesting is that the scales, which they described as having the shape of a factory roof, could be viewed at the micrometer level — that is, each scale tip was positioned about 10 micrometres apart, or about one-tenth the width of a human hair.
Small to us, a micrometre is massive in the world that defines nanotechnology, and this is where previous research on fireflies and other insects had largely focused. But at that level, the structures were observed to have a small impact on efficiency — a few per cent increase at most.
The Belgian team was quite surprised to find much larger efficiency gains at the larger micro-level, and this encouraged them to take their research to the next level.
That’s when Belarouci and his research colleagues in Sherbrooke entered the picture. Their role in the collaboration was to replicate the jagged scale structure of a firefly’s lantern and adapt it to an LED device. They did this using a photolithographic process. It involved coating the top of an LED with a light-sensitive material, in this case a type of polymer, and using a laser to create the factory-roof profile.
“We can do this with most LEDs,” said Belarouci, emphasizing the simplicity of the process. “The advantage is that you can add the coating to an existing LED. You don’t have to redesign the whole thing.”
That they have demonstrated the ability to boost LED efficiency by more than 50 per cent has major implications for a market that’s just finding its stride and a technology already known for being 85 per cent more efficient than conventional incandescent bulbs.
Never mind that LED bulbs last more than 20 times longer and don’t contain mercury, one of the biggest criticisms of compact fluorescent bulbs.
As the New York Times reported this week, prices for LED lights are falling and growth is picking up. It cited the fact that LED technology, despite higher retail prices, accounted for 20 per cent of lighting revenues at Philips last year, and that LEDs are expected to outsell incandescent lights in Canada and the United States in 2014, according to technology research firm IMS Research.
By 2016, IMS predicts shipment of LED bulbs for use in standard residential sockets will hit 370 million units. That’s more than 10 times the shipments reported in 2012.
As for the firefly-inspired coating, the researchers figure that modifying existing LED manufacturing techniques to incorporate the light-boosting layer are achievable and could lead to even better energy savings from LED lights within the next few years.
Has the research caught the attention of industry? “So far we haven’t been contacted,” Belarouci said.
It’s only a matter of time.
And it’s not just LEDs that could benefit from this discovery. “You could use the same kind of concept to improve photovoltaic cells,” he said. In other words, solar cells with the coating could potentially absorb more sunlight and produce more electricity per cell.
It’s something to think about the next time you spot a firefly, or, if you prefer, fairies with magic dust.
Tyler Hamilton is a business columnist for the Toronto Star, Canada's largest daily newspaper. In addition to this Clean Break blog, Tyler writes a weekly column of the same name that discusses trends, happenings and innovators in the clean technology and green energy market. This blog is a personal project started in April 2005. It is not an official blog of the newspaper.
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