Wearable, battery-free device to measure light

Scientists have developed the world's smallest wearable, battery-free device that can measure exposure to light across multiple wavelengths, from the ultra violet (UV), to visible and even infrared parts of the solar spectrum.

When the solar-powered, virtually indestructible device was mounted on human participants, it recorded multiple forms of light exposure during outdoor activities, even in the water, said researchers from the Northwestern University in the US. 

The device monitored therapeutic UV light in clinical phototherapy booths for psoriasis and atopic dermatitis as well as blue light phototherapy for newborns with jaundice in the neonatal intensive care unit. It also demonstrated the ability to measure white light exposure for seasonal affective disorder, according to the research published in the journal Science Translational Medicine. 

The device enables precision phototherapy for these health conditions, and it can monitor, separately and accurately, UVB and UVA exposure for people at high risk for melanoma, a deadly form of skin cancer. For recreational users, the sensor can help warn of impending sunburn, researchers said. "From the standpoint of the user, it couldn't be easier to use -- it's always on yet never needs to be recharged," said John Rogers, a professor at Northwestern University. "It weighs as much as a raindrop, has a diameter smaller than that of an M&M and the thickness of a credit card.