A card may include a photoconductive layer and an electrophoretic layer. The impedance of the photoconductive layer is lowered when struck by light from the light-emitting layer. Where the impedance of the photoconductive layer is lowered, the electrophoretic layer may be addressed by an applied electric...http://www.google.com/patents/US6753999?utm_source=gb-gplus-sharePatent US6753999 - Electrophoretic displays in portable devices and systems for addressing such displays
