Researchers have created wireless, battery-free sensors that can monitor exposure to solar radiation in real time. Their miniature devices provide a portable and flexible method to track light exposure that could prove useful in monitoring doses of ultraviolet (UV) radiation during outdoor activities and optimizing light-based treatments for skin conditions. High exposure to UV light can lead to an increased risk of melanoma and other skin cancers, which together cost over $8.1 billion a year in the U.S. and are projected to reach "epidemic proportions" in the country. Light exposure can also be therapeutic, however: the use of blue light therapy has become a standard-of-care treatment for infants with jaundice - a liver condition that affects 50% to 60% of preterm infants. Existing UV monitoring devices suffer from various drawbacks such as limited battery life, which has hindered their broader use. To overcome these obstacles, Seung Yun Heo and colleagues created a low-cost technology that consists of flexible, adherent sensors that can monitor various forms of radiation. It features a "system on a chip" design, allowing wireless, smartphone-based access to an individual's sensor-read solar exposure data. Healthy volunteers wore the sensors during outdoor recreational activities (including walking and swimming) over a four-day period, and the authors observed that the devices remained functional and reliably recorded UVA solar radiation doses. What's more, the sensors were fabricated in different shapes and sizes, and could capture UVA and UVB exposure for clinical phototherapy. They also successfully monitored light exposure in infants undergoing blue light therapy for jaundice. Heo et al. say that the sensors even remained functional after a cycle through a washing machine.