I recently replaced my headlight low beams as previously the right front passenger light went out. Now, after about a month, the same light is out again. I have HID discharge bulbs not halogen ones if that makes a difference. I tested the car battery and it seems fine. Any ideas what to check next? Thanks.

2008 Lexus ES350

Update:

 

Did you use a quality D4S bulb? Cheap ones tend to have problems.

 

More to add to this. I switched my headlights and now the drivers side is out. So that points to a bulb issue. The only thing I'm not sure about is the bulb turns on sometimes when I start the car, and then goes out after a few minutes. Visually inspecting the bulbs neither one looks "blown" they appear to be in similar condition. Now I believe I have a secondary issue. Both my low and high beams on my passenger side are always more dim than my drivers side. What could be causing this?

 

Are you wearing clean gloves while handling the bulbs? Any oil contamination on the bulb, including the oil from one's skin, will lead to premature failure.