I have a 2002 Accura with HID headlights. I've noticed, fairly recently, that both headlights are much dimmer than expected. I'm fairly sure this is a recent occurrence. My wife's car also has HID lights, but are much brighter.

It's been hard to find good information on troubleshooting, although I'm sure it's out there. Just that sorting through general headlight articles, BS from typical internet urban legends, etc has become pretty tedious.

I have a couple of specific questions that will help troubleshoot the problem rather than wasting a lot of time and money trying various "solutions".

  1. Does the brightness of a Xenon bulb depend on voltage? My battery voltage is fine, and the alternator works as expected, but I haven't gone to the trouble of checking the voltage at the headlights yet - it's not so easy to get to. Since both headlights are the same, I'm assuming it's not the bulb or ballast, unless...
  2. Do xenon bulbs get dimmer with age? I've read articles that say both yes and no, but nothing from a reputable source so far.

I've read about refinishing the outer lens. I cleaned mine pretty well, but although they seem a bit cloudy, they are still pretty transparent, I think. Any suggestions are appreciated, although solutions like "replace the ballast", etc without explanation will be mostly ignored.

  • Welcome to Motor Vehicle Maintenance & Repair! Commented Dec 7, 2019 at 15:53

5 Answers 5


HID bulbs don't dim over time like halogen bulbs simply because they don't have a filament. HID bulbs produce an arc. As a filament deteriorates, it deposits a metallic film inside the bulb. That's what reduces light output. That doesn't happen with HID.

HID systems have an ignitor, ballast and bulb. The ignitor generates very high voltage to start the arc. Then the ballast takes over to provide steady power to keep the arc going. Some setups have a separate ignitor and ballast while others incorate the ignitor into the bulb or into the ballast.

A poor ground would cause the ballast to provide less power to the ballast. But each headlight has its own ground so it doesn't make sense that both would be bad. Since you didn't specify which model Acura it's hard to know whether you have individual ignitor/ballast. The 02 TL has separate units and they're very expensive. If the ignitor was bad, the bulb wouldn't light. So start by checking voltage drop on the ground connections. If it's good, you may have to replace the ballast. I assume you don't have clouded lenses.

  • I do have a TL. I once had one light that would go on and off, and by switching bulbs found that it was not the bulb. I bought a ballast kit from Amazon, which looked exactly like the original. It came with the igniter (fortunately) because when I tried using the old igniter, it still didn't work. New igniter was the fix. As for your assumption... By lens, do you mean the outer plastic cover? They were a bit clouded, so I cleaned them up - first with fine sandpaper 00 steel wool, and lastly used a random orbital buffer with liquid rubbing compound. I think it's much better now. Commented Dec 8, 2019 at 0:09

Your vehicle is 17 years old and the problem is that your HID lamps have aged and no longer produce as much light as they did when newer. Most brands are rated at about 2000 hours of lifetime which would easily be exceeded in 17 years.

HID Life Expectancy

  • Thanks, but that wasn't the answer I'm looking for. All the article says is that this is the lifespan. But it doesn't say what happens when this point is reached; does it get dimmer, or does it simply burn out? An important point, in that if it burns out, then replacing the bulb will only give me a longer lasting dim light. Commented Dec 7, 2019 at 1:54

So, I've learned a lot about old car headlights, and determined the problem, and a solution that may or may not last...

The outer lens was simply cloudy, and blocking the light. I ended up using wet sanding, going from fairly fine (200 - 300 or so) to extra fine (up to 3000, IIRC). I used a random orbital sander for most of it, but at the end, did it by hand.I then used some fairly fine auto rubbing compound to finish it up. This all made it look good and work well... for about a year and a half.

Much of the damage is caused by the sun's UV rays, So, I redid it, first doing a bit of reading on techniques, and how the kits you can buy work. But I had a lot of what I needed, so I didn't want to buy a kit.

Recently, I redid it, using a wider selection of sandpaper, up to about 5000, I think. It looked pretty good,but I used some plastic polish (Meguiar's G12310 PlastX Clear Plastic Cleaner & Polish) which helped get rid of the very fine imperfections.

To try to make it last longer, I finished it up with 3M Quick Headlight Clear Coat from Amazon. This wipes on, and made it look even better, like new. Hopefully, it will last longer, but at least I know what to do if it doesn't.


I actually measured decreased light output from a 5 year old Phillips D3S HID lamp compared to a new HID lamp of the same make and part number. Using a Foot-Candle light meter I measured the "Bright Center spot" of the new and old HID lamps from 10 feet away. The highest Foot-Candle readings were: 200 FC for the 5 year old lamp and 500 FC for the new lamp. New lamp on left, old cloudy lamp on right

  • new lamp on left, old cloudy lamp on right
    – TomB
    Commented Dec 10, 2023 at 20:28

Yes absolutely they dim. Eventually the xenon gas leaks out and what you you have left is arc light. Still bright but not xenon bright.

Nothing lasts forever.

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