Glowing Butterflies Shine With Natural LEDs

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"We must have been doing something right," he said. "Knowing that nature can confirm the inventions we came up with certainly gives a good feeling."

Mirrors and Crystals

High-efficient LEDs reflect and direct light outward, including light that would be lost with traditional LEDs.

The first trick is the use of specialized mirrors called distributed Bragg reflectors (DBRs), which are multilayered mirrors that bounce back light of a specific wavelength or color.

This multilayer mirror is placed underneath the LED, meaning that any light of the desired wavelength directed downward is reflected upward.

The second trick is the use of photonic crystals, which prevent light of the desired wavelength from going sideways or getting "trapped."

The result is better control over the flow of light and thus a more efficient LED, Vukusic said.

Butterfly Wings

Wondering how the swallowtail butterfly controls the flow of light, study authors Vukusic and Hooper examined a wing under powerful microscopes.

They found that each wing contains hundreds of thousands of tiny scales. Each scale has a slab on it where fluorescent pigment is stored.

Fluorescence is the process by which high-energy ultraviolet radiation is absorbed and reemitted as a lower-energy visible radiation. In the case of the butterflies, sunlight is reemitted as blue or green light.

Underneath the pigment slab are layers of reflective surfaces—natural versions of DBR mirrors. The butterfly's "mirrors" are tuned to reflect blue-green light.

Like the photonic crystals in high-efficient LEDs, the pigment slabs are structured so that blue-green light does not radiate sideways from the slab. As in high-efficient LEDs, the light is directed up and out.

The combined effect of the reflectors and the structure of the slab, explained Vukusic, is a much brighter blue-green fluorescence than could be achieved with pigment alone.

The brighter wings allow the butterflies to better signal to each other, he added.

"Nature has had to come up with very elegant and ingenious design protocols in order to achieve a significant control over the flow of light," Vukusic said. "Those are design protocols which may point the way to newer, better, more efficient systems."

Erchak, the high-efficient-LED pioneer, quipped that the finding "means that butterflies are smarter than MIT students."

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