Pulse-current operation is a technique to modify the spectral energy distribution of the radioactive output of discharge lamps. In high-pressure-sodium (HPS) lamps the color-correlated temperature (CCT) can be increased from its usual value of about 2100 K. when operated on a sine-wave power supply to over 3000 K [1-4], Audible noise is an undesirable effect associated with current pulse fed HPS lamps, even if operating conditions are properly set such that the lamp power frequency does not excite longitudinal acoustic resonance modes inside the arc tube. This noise is caused by two phenomena: magnetostriction and photoacoustic effect. This paper investigates experimentally both phenomena.
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