A photoelectric load control system for applying power to a light or load as a function of ambient light level and as a function of the length of daylight or darkness. The system includes a switching circuit for selectively applying power to the light or load for turning the light or load on and off;...http://www.google.ca/patents/US5895986?utm_source=gb-gplus-sharePatent US5895986 - Photoelectric load control system and method
