No abstract

There are some phenomena in High Intensity Discharge (HID) lamps which have the potential to make the discharge unstable. Discharge instability, can lead to some transients in light intensity or in its periodic form, to annoying light flickering. Instabilities appear in a vast range. Depending on the strength of the source of instability, it varies from a very slight deflection of sodium sheath to extreme deviations of conducting channel from its normal position which can extinguish the lamp as well. In order to detect the existence of such phenomena and predict their potential power, their effects and consequences on the light intensity can be analyzed. This has been done by using a tuned model of the human eye-brain system, to predict the perceptibility of the transient changes of light. The purpose of this paper is to introduce the 'light flicker factor' based on eye-brain model as a measure of discharge instabilities. The implementing method of the model and a proper measuring system for light flicker factor is being discussed. Some laboratory experiments to support this method of measurement are presented.

In order to avoid the acoustic instabilities in metal halide (MH) lamps a proper method is to supply the lamp with a low frequency square-wave current. Due to the topology of electronic ballasts for such an application, there is a high frequency ripple in the current or voltage waveform. It is known that such ripples with sufficient energy at the proper frequency are able to excite acoustic resonance in MH lamps. The threshold value for high frequency ripples in order to excite an acoustic mode and destabilize the lamp is under debate. This threshold is lamp dependent and should be measured experimentally for each lamp type. This paper addresses an automated experimental method to determine the threshold value of the power ripple in a frequency range of 10 -400 kHz. The implementation of the proposed method which is based on the light flicker factor has been explained in a preceding paper. The experimental results show that less than 1 percent of power ripple at the resonance frequency is sufficient to excite a detectable (perceptible to the human eye) acoustic instability.