Pete Vukusic and Ian Hooper of Exeter University in England studied the colored parts of the swallowtail's wings and found that the scales that comprised them contain photonic crystals whose atoms are spaced so precisely that only certain wavelengths of light can pass through. The crystals are also saturated with fluorescent pigments that help them create specific wavelengths of light, visible to us as bright colors.
Tiny, mirrorlike structures known as distributed Bragg reflectors reflect this fluorescent light as well as all the other light the photonic crystal allows to pass through. The result: butterfly wings that transform ordinary sunlight into brilliant greens and blues incredibly efficiently.
Thus what the butterflies evolved to do, scientists have built light-emitting diodes to do, employing the exact same components--photonic crystals and Bragg reflectors--in search of ever better ways to project and direct light. The findings are published in the current issue of Science.