Detection of acoustic resonance in metal halide lamps

To understand the occurrence of acoustic resonance in metal halide lamps is essential for an engineer to design a high-frequency electronic ballast. This paper proposes a simple method by measuring the lamp voltage for detecting the acoustic instability instead of observing the lamp arc by human eyes. The standard deviation in the lamp voltage is used as an index to determine the occurrence of acoustic resonance. With the index, the degree of the lamp arc instability can easily be specified. Experiments are carried out on various 70 W lamps to inspect the influence of the lamp type, the used hours, and the operating power on the frequency spectra of acoustic resonance.