ARCHITECTS and car designers are leading the demand for "smart" windows that can change colour, and hence transmit different amounts of light, depending, on the conditions. Two processes haye been investigated to achieve this:- photo-chromism, where the colour changes when light is shone on the material; and electrochromism, where the colour change depends on an applied voltage. Photochrornic devices do not consume any energy, but the colour change cannot be controlled by the user. Electrochromic devices, on the other hand, need a power source to change the colour, but this change can be adjusted precisely.
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