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newview
Ex .. Ex .. Exactly
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join:2001-10-01
Parsonsburg, MD
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reply to newview

Re: Headlight output degradadation over time?

Is it the actual use that degrades the bulbs ... or simply time?

The reason I ask is that the even though the car is 7 years old, it only has 18,000 miles on it, and most of THOSE miles are daylight driving. I drive it very rarely, preferring to drive my pickup.

So if it's use that degrades the bulbs, I would expect them to last considerably longer that normal use, simply because in my case, they are not used as much.

If it's time that degrades the bulbs, then I guess I'll find out in about a year.



cdru
Go Colts
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join:2003-05-14
Fort Wayne, IN
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said by newview:

Is it the actual use that degrades the bulbs ... or simply time?

Time does have an affect, but it's mainly use. You are very slowly burning the tungsten filament.


aurgathor

join:2002-12-01
Lynnwood, WA
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said by cdru:

Time does have an affect,

What exactly? How?


but it's mainly use. You are very slowly burning the tungsten filament.

To be exact, some atoms from the filament get vaporized and then they can get deposited on the relatively cool glass.
That will:
a) weaken the filament
b) creates a metallic coating inside the glass envelope

This is actually when halogens come into play -- they can react with the metal vapor creating metal halides, and those metal halides will no longer get deposited onto glass, but instead the metal can get re-deposited back into the hot filament.
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cdru
Go Colts
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Fort Wayne, IN
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said by aurgathor:

said by cdru:

Time does have an affect,

What exactly? How?

I guess I should have said vibration over time, presuming the car is driven but the headlights aren't used. If it just sits in a garage, then more or less indefinitely.


aurgathor

join:2002-12-01
Lynnwood, WA
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Reviews:
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Yeah, vibration may have an effect, though I think in normal use its effect is probably negligible in properly designed and installed bulbs.

Can't speak for any other vehicles, but in my Bronco, over 13 years and 150k+ miles, I never had to replace any light bulb other than license plate light, in spite of that a good portion of those miles were night, or off-road driving,
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Wacky Races 2012!