Fish scales light the future

They coat your hands, rod and fishing reel, but ever wondered what makes fish scales from species like sardines, mackerel and herring shimmer and flash?

And come to think of it, what gives beetle shells, butterfly wings and peacock feathers their iridescent glimmer?  

It’s an effect that dazzles the eye and for many years, the explanation has eluded baffled scientists. But now they’ve found an answer, and the good news is that their discovery could revolutionise lighting technology.

Shimmer effect

Shoal of swimming fish underwater.

Image source: Rich Carey
Ever wondered why fish scales shimmer?

It’s all to do with what happens when light hits a “dirty crystal”. Way back in 1958, a scientist called Philip Anderson noticed that when he shone a bright light through a crystal containing multiple flaws, instead of passing right through the object, it bounced around inside. The many different layers of the crystal mean that rather than traveling in a straight line, the electrons are diffused through the medium.

Beyond a certain point, if the crystal is too “dirty”, and the movement of the light waves too disordered, the light cannot pass at all. But in less flawed crystals, the light eventually escapes from the object giving it a metallic glow – so called “Anderson localisation”.

Science

Woman in a science lab looking at a test tube.

Image source: darrenmbaker
Scientists are Bristol have been on the case.

Now scientists at Bristol University have discovered that the iridescence in the natural world is the result of light passing through multiple layers nano-crystals – minute structures that produce the same effect that Henderson discovered decades ago.

The different effects we see in nature are courtesy of variation in the layering and arrangement of millions of tiny crystals. So although the multicoloured shine of a beetle shell is different from the silver flash of a sardine scale and the metallic blue glimmer of a butterfly wing, in fact the effect is the result of the same basic principle: that light cannot pass directly through a “disordered” medium.

Refraction

Crystal texture

Image source: theseamuss
Confused? Think about crystals…

For fish like sardines, super reflective scales are perfect for helping to reflect the ambient light of the waters through which they swim. It’s a natural technology that makes them harder for predators to locate. And it all comes down to those crystals, to be specific, birefringent guanine crystals.

Baffling? Definitely, but here’s a simple explanation: Fire a light beam at a birefringent crystal and the light is refracted (bent) differently depending on whether the light source is directed horizontally or vertically (and everywhere inbetween). And the prospect of the development of  a light that beams in multiple directions simultaneously is getting scientists and technologists seriously excited.

Lighting the future

Lightbulb on a green background.

Image source: Rangizzz
Shine on!

And as is so often the case, nature provides the answers to very human problems. As we hunt for ever more efficient ways to heat and light our homes, it appears that nano-crystal technology may hold the key to helping scientists to develop better lighting systems. In an era when global warming threatens and at a time when peak oil makes energy saving a top priority, the discovery of what makes fish scales shine is surely a case of the right discovery at the right time.