Why does the lumen maintenance of sodium-scandium metal halide lamps improve by VHF operation?

摘要

The question why sodium scandium metal halide lamps perform better on VHF (Very High Frequency) drivers than on LF (Low Frequency) CWA ballasts will be addressed with focus on burner aspects. It is argued that at high frequency operation sodium loss is less and the absence of thermal fluctuations in the electrode tip causes less damage to this part of the electrode. The low rate of tungsten evaporation shows that the electrode temperatures are relatively low, indicating that under these conditions thorium is functioning as emitter, both in the anode and the cathode phase.