HID headlights: a little background

I have a 2007 Prius with HID headlights, 54,000 miles. Today I had the headlights changed for the 3rd time, under warranty. First time Jan. '09, 2nd time, Aug. '09, and now, July '10. First time was under vehicle warranty; dealer said replacements had 1 year warranty, so the last 2 times were covered. Today, one of the bulbs was shattered. A little background on HID's: they have no filament like a regular bulb. They operate under extremely high pressure, and when they get old (weak) they can't fire across the hot gas in the bulb, so they go out. When the bulb cools off, they can come back on, and continue to "cycle", til they reach end of life. The only "controller" for these is what is known as a ballast, which an earlier
poster talked about controlling the voltage. This is basically the same system that is used in outdoor lights (streetlights) My own observation: These lights are so bright, that when one goes out, you don't even notice, (until you get pulled over by the police). If you take your car in to have one replaced under warranty, DON'T turn it off til the service person sees that it isn't working, because if he turns the lights back on, and they work, you are out of luck!!