Nataliya Vaitkevich, Pexels

Light consists of individual particles that propagate in waves. The wavelength determines the color and energy of the light.

The human eye can only perceive a small section of this spectrum, approximately the range between 400 and 700 nanometers.

Because of that, we humans are unable to see the infrared range, with its longer wavelengths of 750 nanometers to one millimeter.

So in order to see infrared light, we have needed comparatively bulky night-vision goggles or night-vision devices with their own energy source — until now.

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Infrared contact lenses from China

Researchers at the University of Science and Technology in Hefei, eastern China, have now developed a contact lens that converts infrared light into visible light, enabling humans to see in the dark.

Yuqian Ma and his team have combined conventional soft contact lenses with 45 nanometer particles consisting of gold, sodium gadolinium fluoride, ytterbium and erbium ions.

The upconversion contact lenses (UCLs) convert infrared light with wavelengths between 800 and 1,600 nanometers into visible light, the team wrote in the scientific journal Cell.

The nanoparticles enrich the long infrared light waves with energy. In doing so, they convert infrared light into three primary colors, making them visible to the human eye.

One drawback is that the resulting images are very blurred because the nanoparticles in the lenses scatter the light, which the team was able to partially compensate for by adding additional lenses.

However, the infrared contact lenses are still nowhere near as powerful as night vision goggles, which amplify weak infrared signals, making them visible.

Even better vision with eyes closed

The team first injected nanoparticles into the retinas of mice and their behavior showed that they could see in the dark.

The newly developed contact lenses are much more practical because they are non-invasive — meaning no injections into our retinas.

In tests, humans were able to recognize patterns, letters and flashing infrared signals in the dark. And the infrared lenses work even better with closed eyes, because the infrared light can easily penetrate the eyelids and image generation is not disturbed by normal visible light.

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Animal infrared capabilities

Several animal species are able to perceive infrared light, which is extremely helpful when hunting in the dark. They do not see infrared light as "light" in the sense of human vision. Instead they perceive the heat radiation emitted by objects.

This helps some cold-blooded reptiles such as snakes (rattlesnakes and pit vipers), certain fish (piranhas and cichlids), some amphibians (bullfrogs) and some blood-sucking insects (mosquitoes and bugs) with orientation or hunting in the dark.

Warm-blooded animals — such as humans, other mammals and birds — cannot see infrared light because their eyes do not have the appropriate receptors and their body's own heat radiation would also interfere with the perception of infrared light. 

Big question about the benefits

As fascinating as the Chinese innovation is, it remains to be seen how it could be used in everyday life.

According to the developers, the lenses could be used in surgical procedures, in the field of encryption or cryptography, or for counterfeit protection.

This is because infrared light is what makes invisible features or inks visible on documents, for example.

The lenses could also be used to rescue people in poor visibility conditions because they make heat-emitting objects visible. However, many critics doubt this, as night vision devices are much easier to use, and are also significantly more powerful.

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This article was originally written in German.

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Near-infrared spatiotemporal color vision in humans enabled by upconversion contact lenses