The invention basically comprises: an isolating unit in series with the power line supplying the lamp, said isolating unit automatically disconnecting when the lamp is correctly supplied; a timer; a threshold comparator; a photodetector; a magnetic unit releasing a rod which carries a flag and is arranged...http://www.google.ca/patents/US4580099?utm_source=gb-gplus-sharePatent US4580099 - Device for the remote detection of a failed lamp in a lighting system with a plurality of lamps connected in parallel
