MIT Technology Review

Tuesday, February 12, 2013

A Window that Doubles as a Mirror

And it can switch modes in record speed.

Diginfo reports that AIST has developed a light-controlling sheet that can render a window into a mirror in a matter of seconds. You may be surprised to learn that these switch-hitting mirror/windows are nothing new, in a sense; a division of AIST was actually working on something similar a year ago. But by paring the technology down to a miniscule sheet that affixes to glass--rather than having the technology be embedded in the glass itself--AIST has dramatically scaled back amount of time it takes to toggle between loads.

“For example,” explains a spokesman in the Diginfo video below, “windows in the Boeing 787 take 30 seconds to switch, but with our system, windows of the same size switch in five seconds.”

Why would you want something that can do double duty as a mirror and a window? Putting the glass in mirror mode also serves as a way of tinting the windows. Once you toggle into the reflective mode, there’s plenty of light outside that is no longer getting in. By shutting out sunlight, you can keep a building cooler on a hot summer day, and reduce use of air conditioning and concomitant costs.

The AIST spokesman walks viewers through the anatomy of the window: “On the back, there's an acrylic sheet,” he explains, “and the new sheet we've developed is attached at the corners using tape. There's inevitably a gap of 0.1 mm between the glass and the sheet. We fill the gap with hydrogen, which is produced by the electrolysis of water. In this way, the sheet can be switched from the mirror state to transparent.

There’s a word for this kind of class: “electrochromic” (it’s also known as smart glass, “magic” glass, or switchable glass). In TR’s own pages, we’ve actually been covering this topic for over a decade. See, for instance, “Electronic Windows Shades” and “Let (Some) Sun Shine In”--that last article dating back to 1998. Of course, technology is more easily conceived than executed, and incremental gains can be the difference between a mere concept and a market reality. Which is why AIST’s latest development, though small, is exciting.