These high emission LEDs are an efficient variation on the diodes used in electronic equipment and displays. The University of Exeter, UK, research appears in the journal Science. In 2001, Alexei Erchak and colleagues at the Massachusetts Institute of Technology (MIT) demonstrated a method for building a more efficient LED. Most light emitted from standard LEDs cannot escape, resulting in what scientists call a low extraction efficiency of light.

The LED developed at MIT used a two-dimensional (2D) photonic crystal – a triangular lattice of holes etched into the LED’s upper cladding layer – to enhance the extraction of light. Bragg reflectors were used to control the emission direction. These high emission devices potentially offer a huge step up in performance over standard types. Pete Vukusic and Ian Hooper at Exeter have now shown that African swallowtail butterflies evolved an identical method for signaling to each other in the wild. The wing scales on these swallowtails act as 2D photonic crystals, infused with pigment and structured in such a way that they produce intense fluorescence. Most of this light would be lost were it not for the pigment being located in a region of the wing which has evenly spaced micro-holes through it. This slab of hollow air cylinders in the wing scales is essentially mother nature’s version of a 2D photonic crystal.