Contact lens containing UV dye showing the status prior to and after UV exposure at 50.4 mW m −2 for 30 min. Scale bars = 10 mm.

University of Munich scientists have developed a novel ink for consumer wearables that changes colour when exposed to ultraviolet (UV) light.

The study, published by Advanced Functional Materials, found the ink suitable for a range of wearables, including contact lenses, skin patches, sunglasses and even tattoo ink, giving the wearer an indication of UV exposure. Researchers said various colours can be used and manufacturers can also pre-programme the rate of colour change.

The ink changes colour between wavelengths of 280 and 400nm, which is mostly in the violet range, but it can be mixed with other colours to look like the change is happening in a different colour range, said researchers. This approach offers wearers an easier way to immediately estimate their UV exposure with the naked eye and provides more accurate data for an accompanying app also developed by the research team.