Very fine corrugations or lines can, via the physics phenomena of diffraction or interference, produce beautiful colours. But in the case of the fly, no colours were being emitted — in fact, no light at all was being reflected. All the light landing on the front surface of the fly's eye was entering the eye. It occurred to them that they could replicate this on solar panels, which usually reflect about 10% of the Sun’s rays instead of absorbing them all to produce electricity. By copying the fly’s eye, they worked out the refractive index of the glass on the front of the solar panels, and have now made panels that absorb all the light that lands on them and reflect none — producing 10 per cent more power. As noted by Australian TV scientist Dr Karl, it took a lot of temperature and pressure and fancy manufacturing processes to end up with this finely corrugated plastic — but in the case of the fly, nature did it with organic chemicals at room temperature and pressure.[i]
The relationship between the light of the Sun, the eye, and usable energy continues to amaze us – and there is much more to learn yet.
Top left: Source: mikroman6/Getty Images, courtesy of abc.net.au
Top right: “Scanning electron micrograph image of a 45 million year old fly's eye, showing 4 facets, each with the anti-reflector on the surface.” Photograph: Natural History Museum https://www.theguardian.com/science/gallery/2007/jul/24/1#img-8 [GD4011614@Scanning-electron-mic-5558.jpg]
[i] See: http://www.abc.net.au/science/articles/2015/12/01/4361433.htm