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If you’re using the sun to power a mobile device that you’re carrying with you, it only makes sense to put the solar cells on something you’re wearing that will be receiving a lot of sunlight. With that in mind, researchers from Germany’s Karlsruhe Institute of Technology have created a pair of sunglasses that generate electricity via solar cells that double as their lenses.

Organic solar cells were chosen instead of more traditional silicon cells because they’re transparent, flexible, lightweight, and can be manufactured in a variety of shapes and colors. Each solar cell lens weighs about six grams, is 1.6 mm thick, and was made to fit into a set of commercially-produced sunglass frames.

Those frames also feature added electronics in the temples, including a microprocessor, two sensors and two displays. The lenses power those electronics, which measure and display the current illumination intensity and ambient temperature as bar graphs. Although they work best in direct sunlight, each lens still generates 200 milliwatts of power under indoor illumination down to 500 lux, which is about average for most offices or living areas. Although 200 mW may not sound like much, it’s enough to power a device such as a hearing aid or a step counter.

The technology could conceivably also be applied to the windows of buildings, where it would generate much more power.

A paper on the research was recently published in the journal Energy Technology.