Originally indicated as an alarm alert in a 1990s US publication, this circuit can be used as a shield to control a strobe lamp. The sensor is a optocoupler with LDR.
This circuit, from Motorola 1976 documentation, uses a common field effect transistor at the time....
September 2016 - can already be found at Mouser Electronics new integrated circuit from Texas...
This is a single transistor stage for a phototransistor. The circuit is suggested by Texas...