HID headlights

Owners with HID headlights recently received a letter from Toyota telling the high cost of bulb replacement and tips on how to make them last longer. My question is about the use of high beam, which was not mentioned in the letter. When I try it in my garage, the high beam seems to be ADDED to the low beam instead of replacing it. Are there two filaments? Does use of high beam add heat and shorten bulb life? How do these things work?

probably two bulbs…check out this web page for more information…