In an electronic flash device used as an artificial light source in photography, a liquid crystal plate or window is disposed in front of a flash unit comprising a flash lamp and a reflector and a voltage is applied or not applied to the liquid crystal plate or window depending upon the type; that is,...http://www.google.com.tw/patents/US4325621?utm_source=gb-gplus-share專利 US4325621 - Electronic flash device
