People who live in hot countries use thick curtains to block the UV radiation from overheating the house inside. It seems though that we all will drop these curtains away! AIST has developed a light-controlling sheet that can switch between mirror and transparent states. This greatly improves the efficiency of air conditioning by reflecting the sunlight instead of absorbing it (like curtains do).
The great improvement is the way that the window changes state - Its not LCDs or some sort of expensive electrochromic glass or exotic material. Instead, its simply hydrogen, produced by water electrolysis:
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.
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