Medium power ceramic HID lamps; problems and opportunities resulting from low lamp power factor

Development of medium power ceramic discharge metal halide (CDM) lamps for retrofit onto existing magnetic ballasted quartz metal halide (QMH) systems has posed many technical challenges and forced certain design choice trade-offs for operation on systems originally meant for QMH lamps. The electrical root cause for the trade-offs is the lower power factor (Pf) of the CDM lamps compared to the Pf of QMH lamps. This paper explores the basic physics of the arc plasma and how the high CRI and high efficacy CDM lamps necessarily have power factors lower than their quartz counterparts. Two design approaches that manage the low Pf issue are discussed.