I could be wrong, but any HID or Xenon lamps that I have ever worked=20 with require a burst of very high voltage to initiate the plasma arc=20 inside the lamp. This voltage is many thousands of volts and is=20 often very high frequency so as to require a very small series=20 inductor to the main DC supply. This ignition arc is most likely what you are seeing when that=20 initial flash of light occurs. As an aside, the early multi-kilowatt Short Arc Xenon Lamps that I=20 used to work with use a separate high-frequency exciter made by, I=20 think, Siemens. This was a metal box with a thick copper bar about=20 3/4" wide by 1/4" thick by about 4" long passing through a hole in=20 the middle of the box. One end of that bar was at ground potential,=20 the other end had 15kV on it. One could draw a very nice arc from=20 ground to that end of the bar. It was fun to play with! But that gives you an idea of how high the frequency was. Anyway, I suspect that it is that very high voltage, high frequency=20 arc that is causing your problems. dwayne At 10:58 PM 2/16/2015, Neil wrote: >Recently got and old car roadworthy and it has HID headlights in it. >The bulbs have an interesting behaviour in that when first turned on, >they emit a quick flash of light, then instantly dim, and slowly >brighten back up to operating brightness. What's not good is that every >so often, that initial flash causes enough of a power surge to knock out >the ECU --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .