Remote dimming control system for a fluorescent ballast utilizing existing building wiring

Abstract

A system is described for remotely controlling the dimming level of ballasts for fluorescent lamps through standard two-wire AC power wiring normally used within buildings. The system makes use of a unique dimming control that creates a small positive-negative voltage asymmetry, or DC offset, and encodes this control signal onto the power lines that supply the ballasts to be dimmed. The control unit can be integrated with a wall switch as part of a variable dimming control to supply “local” remote control. It can be interfaced to a building control computer. A small decoding module preferably located in the lighting fixture near the ballast recovers the control signal from the applied asymmetry of the power voltage, processes it if necessary, and feeds it to the ballast. To minimize power losses in the dimming control, a DC offset of zero volts, or no asymmetry, produces full light output. For full dimming, an offset of about 15 volts is used. The resulting maximum dissipation is only a few watts when dimming up to six, 32-watt fluorescent lamps. The advantages include savings in re-wiring costs, higher power factor levels, lower harmonic distortion and lower radio frequency interference compared to other two-wire dimming methods.