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Fish skin points to better LEDs

Scaly secret to camouflage, and that's no red herring

School of six finger threadfin fish

A trick of the light evolved by silvery fish to avoid predators could help improve optical devices like LEDs, according to a study in Nature Photonics.

While polarisation has many applications in photonics, non-polarising devices are also important. The research – abstract here – took a look at how fish such as sardines and herring reflect light without polarising it.

PhD student Tom Jordan from the Bristol Centre for Complexity Sciences, and his supervisors Professor Julian Partridge and Dr Nicholas Roberts in Bristol's School of Biological Sciences, found that these fish avoid reflecting polarised light by having two types of reflective crystals in their skins.

The crystals are guanine, which as Discovery points out is also a component of guano. A single guanine crystal layer in the scales would polarise the light reflected, which would also “dim” the reflected light.

However, with two types of guanine crystal in their skins, the light isn’t polarised. The resulting higher reflectivity is a defence against predators, as Dr Roberts explained: “We believe these species of fish have evolved this particular multilayer structure to help conceal them from predators, such as dolphin and tuna.

"These fish have found a way to maximize their reflectivity over all angles they are viewed from. This helps the fish best match the light environment of the open ocean, making them less likely to be seen.”

In photonics, this property could be used to make more efficient low-loss devices and brighter LED lamps, the researchers say. ®

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