Fluorescent Ruby Red Roofs Stay as Cool as White

Elementary school science teaches us that in the sun, dark colors get hot while white stays cool. Now new research from Lawrence Berkeley National Laboratory (Berkeley Lab) has found an exception: Scientists have determined that certain dark pigments can stay just as cool as white by using fluorescence, the re-emission of absorbed light.

The researchers tested this concept by coloring cool roof coatings with ruby red (aluminum oxide doped with chromium). Led by Berkeley Lab scientist Paul Berdahl, they first 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. Their results were published recently in the journal Solar Energy Materials & Solar Cells, in an article titled “Fluorescent cooling of objects exposed to sunlight—The ruby example.”

Substantial research over the years from the Energy Techology Area’s Heat Island Group has found that reflective roofs and walls can cool buildings and cars. This reduces the need for air conditioning and mitigates the urban heat island effect. By reflecting the sun’s rays back to space, these cool materials also release less heat into the atmosphere, thus cooling the planet and offsetting the warming effects of substantial amounts of greenhouse gas emissions.

However, wider adoption of cool roofs has been hindered by aesthetic considerations. “We’ve heard many times (from roofing materials manufacturers), ‘We can’t sell white or pastel roofs; our customers want dark green, dark brown, and so on,’” Berdahl said.

Read the full article at the Berkeley Lab News Center: Ruby Red Roofs Stay Cool