# Why do headlights last so long?



## DimBeam (Dec 16, 2005)

There may well be a obvious answer to this question but here goes.
Why does a common auto headlight which obviously is incandescent able to last hundreds if not thousands of hours before the bulb blows out? A SureFire bulb is rated at 30 hours or so. Is it because the Surefire is overdriven? Or is it because a headlight receives a steady stream of power as opposed to a flashlight which has the battery slowly draining.Why can't they make a Incandescent bulb that lasts at least half as long as a headlight. I am missing something here and I am sure there are those in this forum who can explain this.Thanks


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## DreamScape (Dec 16, 2005)

Great Question DimBeam. I'd only be guessing if I answered, so I shall wait too.


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## JonSidneyB (Dec 16, 2005)

I am thinking a couple of things here.

For thier size, Headlamps are rather dim. They have to be or we would be blinding other drivers all the time. 

In many of my lights we are getting many many times the brightness per ounce.

Another thing to note. You brighter yet house hold bulbs probably do not last as long as your autolamps as well.

Last point. I live in a rural area and use lights heavily. I have changed 1 flashlight lamp in a year and have changed a pair of auto lamps this year.

It seems the same to me.


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## HarryN (Dec 16, 2005)

The filaments on an auto bulb are pretty heavy duty - it has to withstand a lot of shock and vibration. From a practical standpoint, the energy efficiency of an auto bulb is not being pushed very hard in terms of Lumens/watt, partly because you have a pretty much endless supply of power from the alternator.

Changing the light bulb on a car can be quite a time consuming process, and expensive if done by a shop. Some car companies provide essentially free bulb changes on their cars for 5 + years, so they really prefer to use ones with long life.

You would be surprised just how little an auto head lamp is actually on, compared to how much time we think we spend in autos.


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## mossyoak (Dec 16, 2005)

and they have a halogen cycle


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## fivemega (Dec 16, 2005)

In order to keep a car bulb shock proof, fillament temperature must be cooler and that means lower efficiency.
A car head lamp can handle a lot of overdrive if used without motion.


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## gadget_lover (Dec 16, 2005)

They really don't last as long as they appear to. 50,000 miles at 60 mph is only 800 hours. Most of us drive primarily during daylight hours, so the headlights may be on only a few hundred hours during the life of the car.

The headlight uses a nice thick, well supported filament. It's somewhat shock cushioned by the modern car's suspension. It's underdriven by quite a bit. The modern car headlight is halogen which lets them run hotter (brighter) without the filament burning away. Older headlights were simply in a vacuum. 30 years ago it was not unusual to replace headlights every few years. 

As someone mentioned the car headlight is not that effcient. It uses 25 to 55 watts to make the same light you get from a 12 watt Surefire.


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## tron3 (Dec 16, 2005)

In the same "light" of this question, why do street lights last so long?

Same reasons I guess. Only on during the night. Thicker filiment. Built to last. Under driven, etc.

I wonder if the chill factor of winter has any impact while driving with lights on. Talk about your heat sinks.


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## DimBeam (Dec 16, 2005)

I still have not gotten a good answer to the second part of my question.Why can't a flashlight bulb be made just as durable and long lasting. Better filament? I refuse to believe it can't be done. It should just be a matter of building down to a smaller scale. It also could be Maglite's salvation in answer to the onslaught of LED lights.


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## JonSidneyB (Dec 16, 2005)

Because we want both Small, Bright, and efficient at the same time. These first three items are in conflict with each other. You add the other part and you really have problems.

And I have had as good of luck with my flashlights as I have my headlights.


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## yellow (Dec 16, 2005)

tron3 said:


> In the same "light" of this question, why do street lights last so long?


mainly because they get alternate current (increases lifespan by minimum 10 times)

The "whiter" the output, the hotter the filament has to be. Thats why most of normal flashlights put out some kind of yellow/brown light. SFs put out very white light, so these bulbs are driven very hard + the lifespan is a worst case number. My actual 9N bulb surely has more than 100 hours (the ones be4 also).

There are "new" whiter car bulbs around here. The instructions state a reduction in usable time.


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## zespectre (Dec 16, 2005)

I also think that most people don't use the headlights nearly as much as they think they do. For example I use mass transit during the week, maybe make one trip to the grocery store a week (say 10 minutes total headlight time -in the fall and winter- but not in the spring and summer) and then some night driving (2 hours tops) per weekend. That adds up to roughly 110 minutes of headlight time. 

Add some trips to NY and back (I prefer to drive late at night) about 5 hrs each way

Add in bad-weather headlight time (rain, fog, etc)

I get a rough estimate of 150-200 hours of headlight use per year. (vs about 1,400 hours for my desk light at home).

Most auto headlamps are rated for 750-1000hrs (some rated up to 1500-2000 hrs) so that gives us a range from 3.75 years up to a possible 10 years of rated time.

Now on the other hand, I run Sylvania Silverstars on my 97 Jeep Cherokee. Due to the extra bright design they are only rated at 150 hours and I put them in last November so by my own calculations I am already be past that mark and they are more expensive than standard bulbs to replace but when they do blow I'll be putting the same thing in again because they were a stunning improvement over the stock headlamps.

I think flashlight bulbs are like the Silverstars, running right in that top right corner of the performance graph "envelope" which is, unfortunately, where the postage gets cancelled.

Oh, and some streetlight designs actually have two bulbs and the second one kicks in when the first one dies (mostly the big highway lights).


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## IsaacHayes (Dec 16, 2005)

Notice how the headlights die in cars with DRL. They use a lower voltage and keep them on all the time.

Mine doesn't have DRL, and is one of the easiest headlights to replace. Just reach in, turn, unclip a wire. A friend's sunfire you had to take the whole headlight out and all this other crap.

Headlights do put a lot of light out light, it's just the reflectors don't focus it very tightly. A Thor does, and uses an auto bulb. 

They have to deal with a lot of varrying voltages. Right now it's cold and this new alternator is running at 17volts (eek!) but no bulbs have burned out yet. My headlights look like HID (overdrive, plus I have 60watt lowbeams) they are so white right now.

They aren't in such a small space that gets hot, so they do get more air.


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## cobb (Dec 16, 2005)

Ive often wondered the same thing. My parents delivered newspapers and frequently left their lights on after light and drove to work. THeir cars do not have driving lights like the newer ones do, so they drive with them on anyway. Seems the best way to get a light to go out after a year is to hit that side of the car or give it a good jolt. Either hit a mail box or run over the curbing. Hey, you delivery 500 newspapers from 3 different companies 7 days a week for 15 years on a rural route it happens. Onetime we hit a bale of hay that fell off a truck. They replaced a few relays, switches about the same time they replace the lights. Now fog/driving aux lights would die after a week. 

The other arguement here is good regarding the spot lights using the same h3 bulb some lights use. I think since with a car the system with the constant current and voltage from the car keeps the halogen cycle going and the suspension of the car makes the ride soft vs dropping a flashlight. Also cooling has to take in here too. I use to have a halogen reading lamp that uses h3 bulbs and weekly it would fail. I would open it up and find the base of the bulb was all blue looking. I added two muffin fans to the lamp housing and it lasted a few months before failing. I also suspect that played a role for the fog/driving lights as to why they burned out frequently.


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## PhotonBoy (Dec 16, 2005)

The headlights on my sister's 1996 Plymouth Voyager have never been replaced; that's almost ten years now. On the other hand, the Daytime Running Lights are a pain in the butt. They keep burning out about every 10 months or so. You have to be a very patient ambidextrous acrobat in order to change them. The access hatch is located in the fender immediately ahead of the front tires. It pains me just thinking about it.


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