Test results from high intensity discharge lamps with current supplied at 50 Hz, 400 Hz and modulated between 15 and 35 kHz

In this paper, test results on commercial available high pressure sodium (HPS) and metal halide lamps supplied with current at different frequencies are discussed. These results are useful for discharge lamps with electronic ballasts. These lamps show acoustic resonances, so that certain frequencies must be avoided in the supply current. Measurements were carried out at input power and light output on HPS and metal halide lamps in the range of 125 to 400 Watt. All measurements are compared with the 50 Hz supply current case. One series of tests was executed at 400 Hz in order to stay below the fundamental frequency for acoustic resonance. At 400 Hz, HPS lamps produced an audible noise. Another series of tests was performed at modulated frequencies between 25 and 35 kHz; this is above audible noise and the fundamental acoustic resonance frequency. Lamp failure did sometimes occur at certain frequencies between 15 and 25 kHz, depending on the lamp type and was probably caused by acoustic resonance. No significant immediate influence of frequency on lamp efficiency was measured.