An electronic ballast system for operating fluorescent lamps at full and partial brightness is disclosed having a series reactance selectively switched into or out of the system by a reactance switch. The electronic ballast has an input filtering section, a voltage-clamped current source, and an oscillator...http://www.google.com/patents/US4686427?utm_source=gb-gplus-sharePatent US4686427 - Fluorescent lamp dimming switch
