• 08.23.13

Smart Windows That Let In Light But Keep Out Heat Are Almost Here

Up to 5% of total U.S. energy consumption goes out the window, literally. Now, nanotechnology could produce a coating for glass that is affordable and effective at saving energy.

Smart Windows That Let In Light But Keep Out Heat Are Almost Here
[Image: Windows via Shutterstock]

Windows are good for gazing–but they’re an energy efficiency nightmare. In the winter, they let out warmth that you want to keep inside. In summer, they let in too much heat, forcing you run the AC for hours. It’s estimated that 4% to 5% of the U.S.’s total energy consumption goes out the window, which costs about $50 billion a year.


There are plenty of “smart glass” solutions on the market that aim to save energy. By running a small current through electrochromic glass, you can get a darker window that stops light and heat from entering. The problem is that the window is then, well, dark: You sacrifice what you do like (sunlight) for what you don’t (an unbearably hot room).

There could now be a way of having the best of both worlds, though. Scientists at Lawrence Berkeley National Lab, in California, have developed a nanocrystal coating that gives more control over the light spectrum, and therefore how much near-infrared light (which produces heat) and visible light (the stuff you like) enter a room. The clever bit is that the window appears completely clear, even when little heat is entering.

“When used as a window coating, our new material can have a major impact on building energy efficiency,” says Delia Milliron, who led the work (she talks more about it in the video below). The researchers write up their findings in a recent issue of the journal Nature.

To control the glass, the researchers currently flip a switch to apply voltage. But Milliron told Business Insider that it should be possible to link the glass to a climate control system, so it would respond automatically to conditions in the room.

More importantly, Milliron says the new smart glass is cheaper than current technologies, because it doesn’t involve any special hardware. To make the window smart, all you need to do is apply the film, then heat it to a high temperature.

The Berkeley team still needs to build the system around the glass and then it would have to find a path to the market. So it could be a while before we’re using it in our homes and cutting those air conditioning bills.

About the author

Ben Schiller is a New York staff writer for Fast Company. Previously, he edited a European management magazine and was a reporter in San Francisco, Prague, and Brussels.