Taking the form of an ultra-thin film, it can be applied directly to glasses to act as a filter, needing only a simple laser to convert infrared light into images the wearer can see.

The researchers' groundbreaking film is based on nanocrystal technology that they've been working on for a number of years. These tiny particles are hundreds of times thinner than a human hair, and work by converting incoming photons from infrared light into higher-energy photons on the visible spectrum.

In 2016, the team succeeded in fabricating one of these nanocrystals onto a plane of glass for the first time. This was seen as the first step in developing an array of many tiny photon-converting crystals that together could form a film that changes the way the human eye perceives light. In continuing this work, the scientists have now produced a prototype version of this film they say is lightweight, cheap and easy to mass produce.

"We have made the invisible visible," lead researcher Dr Rocio Camacho Morales said. "Our technology is able to transform infrared light, normally invisible to the human eye, and turn this into images people can clearly see – even at distance. We've made a very thin film, consisting of nanometre-scale crystals, hundreds of times thinner than a human hair, that can be directly applied to glasses and acts as a filter, allowing you to see in the darkness of the night."