A highly reliable and economical traffic signal has only one light-emitting display section having two or more semiconductor thin-film EL plates of different colors such as green and red stacked one on top of the other. Green and red can be displayed by causing one of the EL plates to emit light and...http://www.google.de/patents/US4857920?utm_source=gb-gplus-sharePatent US4857920 - Combined traffic signal with stacked EL elements
