AIST has developed a light-controlling sheet that can switch between mirror and transparent states. Using this sheet on window glass saves energy by effectively shutting out sunlight, greatly reducing the load on air-conditioning.
“Until now, switching has been done with glass. But with this sheet technology, you can switch a window between transparent and mirror states simply by affixing the sheet to the window.”
“On the back, there’s an acrylic sheet, 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.”
As light-controlling glass, electrochromic glass has already been commercialized. But the disadvantage of that is that the temperature of the chromic layer rises, so energy is radiated into the room again as heat. With this new system, light can be controlled by reflection, making it possible to shut out sunlight more efficiently.
“Electrochromic glass, which is switched electrically, works more slowly if the window is large. For example, windows in the Boeing 787 take 30 seconds to switch, but with our system, windows of the same size switch in five seconds. So, another feature of our system is fast switching.”
In this demonstration, the window takes ten minutes to return to a mirror state. But AIST has already developed a material that can revert in 30 seconds.
“This system works in a simple way. It electrolyzes moisture in the air, converting it to hydrogen, which fills the gap to cause the switch. Just by applying 3 V to this part, you can switch between the transparent and mirror states.”
“Ultimately, we aim to use this system in building and vehicle windows. Windshields, by law, must have a transmittance of at least 70% in the transparent state. So, a major hurdle to be cleared is 70% transmittance for visible light. We’re working on this, and we expect to succeed within a year.”