MikeNSX

With my headlights set to Auto, even on sunny days the HID lights turn on briefly when I enter my garage, then I shut the car off, and they go off after being on less than a minute.

My Home Theater projector uses a HID arc lamp and instructions say that once you turn it on, let it on at least 10 minutes for the bulb to come to temperature. It says that turning it on and off quickly can shorten the bulb's life.

Are we shortening our HID bulb life by using the Auto setting?

Mister Bally

Yes.

Mister Bally

I might add that Audi's auto setting photocell does not seem to employ "fuzzy logic" which some other manufacturers do. This keeps the lights on for a defined period. I stopped using the auto setting when I noticed the headlights coming on for a few seconds when driving under bridges.

MP4.2+6.0

different train of thought.

I noticed looking at bulb performace curves at one point that HID brightness falls off meaningfully over time. As I recall it was at maybe 2000 hours or something.

Since I like my headlights crisp and at original factory bright, and Audi has good headlights--at least compared to the Chryler and Ford junk I have experienced and the Toyota mediocrity--I went down the preventative mainteance path with the 2000 C5 with HID's about a year ago. They are long lived enough that the issue of performance degradation can weigh in. Found OEM quality/brand bulbs new on ebay for a fraction of the usual dealer type prices. And sure enough, pulling the old bulbs out, the surface glass had an etched type feel to it you couldn't get off for starters, let alone whatever the internal degradation had been. Meanwhile, put the old ones in the bulb drawer as spares.

To your original post, doesn't surprise me. I also have seen Prius drivers complaining now about their HID headlights too, on top of the all the run away stuff. No surprise to me, since many seem to favor driving around with both them and the fog lights on 24/7 rain or shine. In the end, these things do have a limited life. Longer than the older conventional bulbs, but still... Comon sense says switching affects it as well. The longest lived incandescent bulbs (Guiness records type stuff) have been low wattage ones that just sit there and are never switched on and off. The exact opposite of a harsh automotive environment.

Bunky

Interesting point. So did the "proactive" bulb replacement result in brighter lights on your C5?

I have noticed that the headlights on my '04 seem to be getting dimmer and dimmer over the years and am wondering if a bulb change may help. Or maybe the bulbs are fine, and it's just *me* wearing out!

MP4.2+6.0

It semed common sense observable. I could tell from the D3 to the C5 that the D3 was better. Both use the D2S bulbs as I recall, but the older C5 actually has the fixed lens design with a separate halogen high bulb; i.e. probably not a compromise between low and high. The D3 does have a very nice lighting throw but the C5 is no slouch. Net, after the bulb change the two were much more comparable on apparent brightness in obvious settings like cruising down a darker interstate (low leams only).

I got there too just thinking thru common sense math--a hour a day (night or rain) w/ lights means 5 1/2 years in they have gotten to 2,000 hours already. I am not ten years + on the C5 (a 2000), and by the time I changed them it was probably 3000 hours+ give or take. I haven't looked up the stats lately, but as I recall the brightness fall off was material by then. Average failure hours on a halogen (or worse an incandescent) were lower, so not as likely to deal with the lifetime brightness issue as with HID's. AND, hasn't been thought through yet on LED's, but those cool new LED headlights might not be so bright eight to ten years later, but cost $$$ to replace (like our tailights).