Being Transparent About Sun Safety

The consequences of overexposure to sunlight are understood better than ever. Ultraviolet radiation from the sun is able to deeply penetrate the skin, where it may damage DNA. The mutations caused by this damage have the potential to turn a healthy cell cancerous, and the more sun exposure a person has, the greater the chances are that this will happen. These risks can make summertime activities feel like a game of Russian roulette.

Fortunately, avoiding overexposure to the sun is quite simple. Covering the skin with clothing and using sunscreen is enough to greatly reduce the risks of skin damage. But while it is easy, it is not always desirable. I mean, who wants to wear a long-sleeve shirt and pants to the beach on a 90-degree day? Slathering on a thick layer of slimy sunscreen every couple hours isn’t most people’s idea of a good time either.

These inconveniences lead many people to simply ignore the danger and rub on some aloe vera after the fact. But a group led by researchers at Soongsil University in Korea thinks there is a better option. They have developed a transparent wearable sensor that monitors sun exposure and lets you know when you’ve had enough. That way, people can enjoy the sunshine without going overboard.

The new device tracks exposure to ultraviolet A (UVA) radiation — the type of UV light that penetrates deeply into the skin and causes long-term damage such as premature aging and skin cancer. Most consumer UV sensors are either opaque, uncomfortable, or only track UVB radiation. So the team set out to build something both more functional and more wearable.

The solution contains a flexible photodiode that detects UVA light in real-time. The sensor is constructed layer by layer, beginning with a transparent piece of glass as a base. On top of that, the researchers deposited alternating layers of specially chosen oxide semiconductors. Two n-type materials, tin oxide and zinc oxide, were paired with two p-type materials, cobalt oxide and hafnium oxide. Together, these formed a fully transparent p-n junction, which is the heart of the photodiode that reacts when UVA light hits it.

To make the device conductive without blocking light, the team used indium tin oxide for the electrodes, a material known for its combination of transparency and electrical performance. The final multilayer structure maintained more than 90% transparency in visible light, making it ideal for integration into glasses, watches, or skin patches. Despite its clear appearance, the device exhibited strong sensitivity to UVA wavelengths between 340 and 350 nanometers.

In field tests under real sunlight, the sensor reliably matched professional UV meters. It was paired with a tiny circuit board containing an amplifier and a Bluetooth chip to send exposure data directly to a smartphone. When a user reached 80% of their maximum safe exposure, the system issued a warning.

Although still in the early development stages, this transparent UVA sensor is a meaningful step toward practical, wearable UV monitoring. With further refinement, it could soon make sun safety as easy as checking your phone.