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Contact lenses have enabled people to see beyond the visible light range, picking up flickers of infrared light even in the dark – or with their eyes closed.

The lenses contain engineered nanoparticles that absorb and convert infrared radiation – specifically, a near-infrared wavelength range of 800 to 1600 nanometres – into blue, green and red light visible to the human eye. That is the same trick night-vision devices use to help people see in the dark, but the contact lenses weigh much less and require no additional power.

“The contact lenses would provide military personnel with discreet, hands-free night-vision capabilities that overcome the limitations of bulky night-vision [goggles or scopes],” says at Texas A&M University, who has done related research applying the same nanoparticles – sodium gadolinium fluoride, ytterbium and erbium – to eyeglass lenses.

The new wearables, developed by at the University of Science and Technology of China and his colleagues, don’t provide detailed night vision yet. That is because they can pick up only “high-intensity, narrowband LED” light sources, says Rentzepis, rather than lower levels of infrared light from ambient sources.

“It’s an audacious paper but, using just the contact lens, you wouldn’t be able to read a book in the infrared, or navigate down a dark road,” says at the University of Wisconsin-Madison, who was not involved in the research.

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Instead, in tests on humans and mice, the contacts converted a normally invisible flash of infrared light into what Kats says should be a “big colourful blob of visible light”. Those blobs had uses, however. For example, Ma and his colleagues varied the frequency, number and colour of different light flashes to encode and transmit letters of the alphabet.

This follows a previous study in which the researchers injected nanoparticles directly into the eyes of mice to provide infrared vision. The wearable contacts represent a “safer and more practical approach for human applications”, says Rentzepis. But they still come with potential health and safety risks, he notes, such as heat exposure from the light-conversion process and possible nanoparticle leakage into eye tissue.