Research Assistant Sharon Chen and Physicist Paul Berdahl hold up their prototype coating made from ruby powder and synthetic ruby crystals at Lawrence Berkeley National Laboratory on Wednesday, September 7, 2016 in Berkeley, Calif. 09/07/16
Courtesy Berkeley Lab/Marilyn Chung Research Assistant Sharon Chen and Physicist Paul Berdahl hold up their prototype coating made from ruby powder and synthetic ruby crystals at Lawrence Berkeley National Laboratory on Wednesday, September 7, 2016 in Berkeley, Calif. 09/07/16

Although most building pros have long believed that white roofs stay cooler than those of any other color, new research from Lawrence Berkeley National Laboratory turns that idea on its head. Scientists there have determined that certain dark pigments can stay just as cool as white by using fluorescence, the re-emission of absorbed light.

Led by Berkeley Lab scientist Paul Berdahl, the researchers found that white paint overlaid with a layer of ruby crystals stayed as cool as a commercial white coating. Next, they synthesized ruby pigment to mix into coatings.

This opens the door to darker colors of not only cool roofs but of any object that is subject to prolonged periods of sun exposure, including vehicles, ships, storage tanks, and PVC piping. “We do think cars will be a likely application,” Berdahl said. “And it’s not just a matter of comfort or saving energy by avoiding AC use. We learned from colleagues that with electric vehicles, the battery lifetime is degraded by higher temperatures, so if you can keep the automobile cooler with use of a suitable coating then it extends the life of the battery.”

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