Defining acoustic resonances in dimmed HID lamps using a finite element model

The first eigenfrequencies of a 150 W HID lamp were determined. The power reduction applied to a gas-discharge lamp is a complex phenomenon which tempts to shift acoustic resonance modes to lower values. Assuming this, electronic control gear manufacturers interested in dimming should preferably avoid the use of HF sine wave in their ballasts. The presented model is giving promising results and the experimental method developed is simple and accurate. Nevertheless, some adjustments and a better identification of the measured modes needs to be done in order to verify if the eigenfrequencies shift predicted by the model are accurate. We expect to be able to present more data for an extended range of lamps and operating power in the near future.