17 Jun 2002
Electrochromic windows that change colour when a voltage is applied have been installed in the Stadtsparkasse bank in Dresden, Germany.
When a voltage of about 3 volts is applied to the windows, they change from transparent, when they transmit 50% of incident light, to a bluish colour, when just 15% of the light is transmitted. Trials in Germany have found that the windows can halve the normal air-conditioning expenses in an office.
The glass, called E-Control, has been developed by Pilkington Glass in the UK. A polymer containing the electrochromic compound, tungsten trioxide, is sandwiched between two panes of glass, which are each coated with transparent electrically conducting films. The applied voltage alters the electric conduction of the polymer and hence its optical properties.
According to an article in the November 1999 issue of Opto & Laser Europe magazine, this is the first commercial installation in a building for electrochromic windows. Previously this glass has been limited to rear-view mirrors in luxury cars because it is difficult and expensive to produce in large sizes.