Experiment synthesis and characterization of acoustic instabilities in high intensity discharge

High intensity discharge lamps comprise a gas encapsulated in a transparent vessel, in which a light emitting discharge arc is established. The lamp operation necessitates a driver that provides an energy saving and cost reduction potential when the frequency of the alternating current is tuned from the commonly used low frequency range to a higher frequency range. However, such an operation can result in low frequency luminous fluctuations, lamp extinction or even destruction. The excitation of acoustic resonances in the high frequency range is the reason for the instable behaviour; therefore a predictive model was established in order to give us at which frequencies light flicker can be expected. Moreover, we conducted an experimental study, which allows the electrical detection of frequency regions, in which the discharge arc behaves instable. Furthermore, an optical system is incorporated to record images of the discharge arc during stable and instable operating conditions. The results enable a considerably better understanding of the flicker phenomenon in HID lamps and facilitate the development of energy efficient drivers.