Question: do xenon bulbs dim over time?
Answer: Yes, HID Xenon lamps get dimmer as the lamps age. It has nothing to do with the ballast. The typical life span rating is 75% @ 1500 hours. Be aware that a lot of newer cars with OEM factory HID xenon headlights, have the beam aim to far down, and the light intensity close the front of the car is excessive.