Atlant’s Column: Stealth Eyes

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Welcome to the section on Micronaut.ch which explores, analyzes and explains fascinating microscopical structures.

moth eye detail

Moths have an ambivalent relationship to light: during the night they love it, because it helps them to navigate, but at daytime they must avoid it under any circumstances, because it would instantly betray them to an army of hugry predators.

Text by science writer Atlant Bieri
Photography by Martin Oeggerli

Overnight, huge moth eyes of the ‘Old Lady Underwing Moth’ (Mormo maura) are the perfect gadget for nocturnal vision, but at daytime they reflect ambient light in all directions – and therefore become a dangerous burden. Like storesigns of a snack bar, the huge eyes indicate birds where to find a tasty bite – and this is not exactly what the moth wants.

Lucky enough for the moth, evolution does not let it run around without high-tech protection. The technology that minimizes reflections of light on its eyes looks stunningly simple, but it is so well designed and efficient that it has quickly inspired scientists and engineers around the world. Today, the resultant man-made solutions are used even in solar technology and on computer displays.

The basic problem of light is, that it is scattered back by the vast majority of objects. It is only because of this reflection, that we see the world. All trees, all meadows, lakes and clouds are basically invisible until reflected light unmasks them and reveals their shape and colour.

If an object swallowed all the light that hits it, it would be clothed in eternal darkness. And this is exactly the state, the eye of the moth has almost reached. For this purpose, its surface is covered with millions of tiny rods. This so-called ‘nipples’ (see below) are tightly packed and are up to 230 nanometres tall in some species. This is the two-hundredth part of the diameter of a human hair.

 

Moth eye lens nipples

The Corneal Nipple Array Provides Natural Antireflective Coating

The ‘Corneal Nipple Array’ is a densely packed forest of tiny rods. The structure blurs the boundaries between air and surface of the moth eye, which means there is actually no more surface to hit – and as a consequence no more reflection. Only one percent of the incident light is reflected making the moths eyes look like two dark brown balls, even under very strong light. Thus, the vision of the moth in the night increases, because ninety-nine percent of the light travels freely to its visual receptors. In moths without nipples, only ninety-six percent of the light reaches the receptor and -even worse- the rest is reflected!

Other animals use the same principle to hide. Jellyfish for instance cover their bodies with a similar kind of rods, too. It makes them almost invisible in the ocean and predators have a hard time to discover the slow jellyfish. Because of these outstanding achievements in nature, human technology is taking advantage of the nipples. Scientists print them onto the surface of solar cells to generate 40 percent more electricity. Likewise, our high-tech computer or mobile phone screens could become anti-glare in the near future.

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Continue reading Atlant’s Column: Cliffhangers, September 2012, or go back to the archive