Sound emissions from pulse operated high-pressure-sodium lamps

Current pulse fed HPS lamps generates audible noise even if the lamp power frequency does not excite longitudinal acoustic resonance modes inside the arc tube. This noise is caused by magnetostriction in conductive parts of the arc tube-supporting frame and in the wires passing through the seal of the outer glass envelope. Conductor dimensional changes effectively couple mechanical energy to the jacket. Photoacoustic effects also cause noise due to pressure waves in a thin air layer surrounding the lamp. This paper investigates experimentally both phenomena and quantifies their contribution in order to minimize acoustic emissions.