I replaced the bulbs because they were dim but the new ones were no better I've cleaned the oxidation off new batter new alternator, when I'm in front of a car i can see my cars shadow and the bulbs were not cheap

4 Answers 4


I would check the battery out put and also check the grounds because these are 2 problems I have seen in the industry.

I hope this helps

  • Welcome to Motor Vehicle Maintenance & Repair!
    – Cullub
    Aug 22, 2018 at 12:32

Have you performed any measurements? I see four reasons for dim lamps:

Age -- As the filament wears, its hot resistance increases and the light output drops. This is a real and measurable behavior. If you replaced them, then you can check this off.

Low charging voltage -- Battery terminal voltage should be 13.8-14.5v or so depending on configuration. Nobody online can measure it.

Voltage drop -- This may be due to contact resistance anywhere an interconnect is made between the source and the load. It could be switch or relay contacts; it could be connectors. If you've measured the battery voltage, measure the lamp voltage. If there is a significant difference, locate the fault by subdivision between the measured points.

Non-electrical -- This could be anything else to do with the composite lamp assembly. Is the aluminized reflector corroded? Is there condensation or deposits inside the lamp assembly? Is the outer surface of the assembly frosted from UV damage? Defects to the lens/reflector don't have to absorb any power in order to make a perceived reduction of "brightness". Diffusion of the lamp's power over a larger area reduces the illuminance.

Lastly, I should mention that people tend to be horribly subjective when measuring things like "brightness" by looking at a light source. Unless you want your assessment to be subject to angular alignment, look at what the lamps actually illuminate. That's how you'll be using them.


While it's going to be awfully subjective in what method people will agree with, it's highly likely that your headlamp assemblies need to be refinished.

I can link a few different sites, like This Popular Mechanics Article here or a YouTube Video here but it's likely best you just visit a well-reviewed local Autobody shop.

The cost of having Headlights refinished professionally, is generally about 1/3-1/2 the cost of buying one headlight. From this point you'll be able to determine if it makes more sense to simply purchase new headlights, or have them refinished.

If you do chose to refinish them yourself, make sure you plan accordingly. Give yourself a good amount of time to complete the project, take your time, and don't skip any steps.

I hope this helps.


Bulbs do not get dim with age so replacing them does not help. What does affect brightness is moisture inside the headlight or aging of the headlight front lens, making it matte instead of clear. I'd suggest looking for those issues instead of focusing on the bulbs.

  • Lamps do get dim -- perhaps not as dim as the OP is experiencing, but it does happen even with halogen lamps. I will not argue that many sources claim that halogens have flat lumen maintenance. I posit that the truth is that the claim is really only true in comparison to non-halogen tungsten lamps. The halogen cycle only reduces filament erosion; furthermore, the redeposition mechanism preferentially acts on the cooler parts of the filament. The result over time is a filament of wildly variable thickness, with correspondingly altered electrical characteristics.
    – DGM
    Mar 30, 2018 at 11:05
  • What about HID (XENON) bulbs? I am trying to find out if these are affected by voltage, or if they either work or don't work. Dec 6, 2019 at 21:06

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