# What makes dashboard lights so durable? **URL:** \ **Category:** Factual Questions\ **Created:** [October 10, 2014, 6:12am UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936 "2014-10-10T06:12:43Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![Darryl\_Lict](https://avatars.discourse-cdn.com/v4/letter/d/7cd45c/32.png) [@Darryl\_Lict](https://boards.straightdope.com/u/Darryl_Lict)\ **Post date:** [October 10, 2014, 6:12am UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/1 "2014-10-10T06:12:43Z")
I’ve got nothing but old cars, the newest of which is a 1984 Toyota 4Runner. I have never had to replace a dashboard light. Since these cars are so old, I assume the bulbs are incandescents. They are also difficult to access, so robustness must be a design consideration. What is it that makes them last so long? I’m guessing they must have super durable filaments or something. They aren’t on all that often as you don’t typically drive all day and I guess they only come on at night, so maybe that’s the answer. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [October 10, 2014, 6:54am UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/2 "2014-10-10T06:54:20Z")
It’s actually not that difficult to make long lasting incandescent bulbs. You just make the glass thick so that it’s not fragile, make sure to seal it well so that air doesn’t get in and cause the filament to burn out, and you use a thicker filament. It costs a bit more, but it’s not difficult. People think of incandescents as being fragile and short lasting because the big light bulb manufacturers for home use made them cheap and fragile. That was for business reasons more than technical reasons. There used to be at least one company making very sturdy and long-lasting home light bulbs, using basically the same techniques (heavy glass, thicker filament). I don’t know if they are still around or not. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [October 10, 2014, 7:38am UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/3 "2014-10-10T07:38:58Z")
One other thing is that there’s usually a bunch of them so you don’t notice if only one or a couple of non-adjacent ones burn out. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [October 10, 2014, 10:20am UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/4 "2014-10-10T10:20:39Z")
tiny bulbs with short, low wattage filaments. the Centennial Light is still working because it barely glows orange. > **[Centennial Light](https://en.wikipedia.org/wiki/Centennial_Light)** > > The Centennial Light is the world's longest-lasting light bulb, burning since 1901, and almost never turned off. It is located at 4550 East Avenue, Livermore, California, and maintained by the Livermore-Pleasanton Fire Department. Due to its longevity, the bulb has been noted by The Guinness Book of World Records, Ripley's Believe It or Not!, and General Electric. > The Centennial Light was originally a 30-watt (or 60-watt) bulb, but is now very dim, emitting about the same light as a 4-watt ni... ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [October 10, 2014, 12:39pm UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/5 "2014-10-10T12:39:03Z")
> [@jz78817](#): > > tiny bulbs with short, low wattage filaments. > > the Centennial Light is still working because it barely glows orange. > > [Centennial Light - Wikipedia](http://en.wikipedia.org/wiki/Centennial_Light) … with a webcam and everything … ---
**Author:** ![JWT\_Kottekoe](https://avatars.discourse-cdn.com/v4/letter/j/3ec8ea/32.png) [@JWT\_Kottekoe](https://boards.straightdope.com/u/JWT_Kottekoe)\ **Post date:** [October 10, 2014, 1:16pm UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/6 "2014-10-10T13:16:39Z")
The lifetime of an incandescent lamp is a strong function of the filament temperature. You can extend the lifetime dramatically by running it at reduced power. Unfortunately, that also reduces the efficiency and drops the color temperature. For an indicator light, you can make that trade off, but not for room lighting. ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [October 10, 2014, 2:30pm UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/7 "2014-10-10T14:30:53Z")
> [@engineer\_comp\_geek](#): > > There used to be at least one company making very sturdy and long-lasting home light bulbs, using basically the same techniques (heavy glass, thicker filament). I don’t know if they are still around or not. Were their bulbs equally bright for the same given current? ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [October 10, 2014, 2:43pm UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/8 "2014-10-10T14:43:35Z")
yeah running the bulb at a lower voltage than it can run at will give a dimmer illumination but last much longer which is fine for indicator lamps. even for bulbs for illumination this works. bulbs sold as long life household bulbs might be 130V bulbs. large bulbs also where the cost of replacing it is more important than the cost of the bulb, like a traffic signal, can be made to a higher quality at a higher cost. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [October 10, 2014, 3:34pm UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/9 "2014-10-10T15:34:54Z")
> [@Really\_Not\_All\_That\_Bright](#): > > Were their bulbs equally bright for the same given current? I don’t remember the company name, so I can’t look them up to see if they are still around or look up the specs on their bulbs. All I can tell you is that the light output was close enough that it wasn’t worth worrying about the difference. ---
**Author:** ![Darryl\_Lict](https://avatars.discourse-cdn.com/v4/letter/d/7cd45c/32.png) [@Darryl\_Lict](https://boards.straightdope.com/u/Darryl_Lict)\ **Post date:** [October 10, 2014, 9:18pm UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/10 "2014-10-10T21:18:54Z")
> [@engineer\_comp\_geek](#): > > It’s actually not that difficult to make long lasting incandescent bulbs. You just make the glass thick so that it’s not fragile, make sure to seal it well so that air doesn’t get in and cause the filament to burn out, and you use a thicker filament. It costs a bit more, but it’s not difficult. Ah, that makes sense. > [@jz78817](#): > > the Centennial Light is still working because it barely glows orange. > > [Centennial Light - Wikipedia](http://en.wikipedia.org/wiki/Centennial_Light) I know about that one and have been meaning to go and see it before it burns out. I was somehow under the impression that its longevity was at least partially due to the fact that it’s never turned off, thus minimizing thermal fatigue (or whatever the term is). ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [October 10, 2014, 9:57pm UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/11 "2014-10-10T21:57:18Z")
> [@jz78817](#): > > the Centennial Light is still working because it barely glows orange. > [@Darryl\_Lict](#): > > I know about that one and have been meaning to go and see it before it burns out. I was somehow under the impression that its longevity was at least partially due to the fact that it’s never turned off, thus minimizing thermal fatigue (or whatever the term is). a big part of its longevity is not having on/off cycles but left continuously burning. it is also being run at much lower than its rated power at the current time. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [October 10, 2014, 10:11pm UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/12 "2014-10-10T22:11:47Z")
Bulb lifetime is proportional to the 16th (!!!) power of voltage, so as others have said you can gain tremendous lifetime by dropping the voltage by just a small amount. The reason why household bulbs last around 1000 hours is [because of a cartel](http://en.wikipedia.org/wiki/Phoebus_cartel) set up in the early days of electric lighting. The cartel is long gone but the effects are still around. That said, there is a tradeoff between efficiency and lifetime, so this wasn’t a completely artificial limit. 1000 hours probably isn’t too far off from the actual optimum. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [October 10, 2014, 10:34pm UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/13 "2014-10-10T22:34:57Z")
Correction: make that _inversely_ proportional. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [October 10, 2014, 10:46pm UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/14 "2014-10-10T22:46:03Z")
> [@Dr.Strangelove](#): > > … > The reason why household bulbs last around 1000 hours is [because of a cartel](http://en.wikipedia.org/wiki/Phoebus_cartel) set up in the early days of electric lighting. … Not to mention them sending hitmen after Byron … ---
**Author:** ![Darryl\_Lict](https://avatars.discourse-cdn.com/v4/letter/d/7cd45c/32.png) [@Darryl\_Lict](https://boards.straightdope.com/u/Darryl_Lict)\ **Post date:** [October 12, 2014, 1:33am UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/15 "2014-10-12T01:33:42Z")
> [@Dr.Strangelove](#): > > The reason why household bulbs last around 1000 hours is [because of a cartel](http://en.wikipedia.org/wiki/Phoebus_cartel) set up in the early days of electric lighting. The cartel is long gone but the effects are still around. That said, there is a tradeoff between efficiency and lifetime, so this wasn’t a completely artificial limit. 1000 hours probably isn’t too far off from the actual optimum. Ha! that’s a fascinating bit of trivia that I never heard of. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [October 12, 2014, 3:13pm UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/16 "2014-10-12T15:13:28Z")
I don’t know how incandescent bulbs are design for automotive instrumentation panels. But various design techniques can be employed to make incandescent bulbs last longer: - More supports. This makes them less susceptible to failure caused by vibration. - Reducing filament temperature. Primarily achieved by using a lower voltage than would “normally” be used. - Special gases that help reduce the boiling-off of atoms from the filament. - Better hermetic seal. - Thicker envelope. ---
**Author:** ![Fubaya](https://avatars.discourse-cdn.com/v4/letter/f/c2a13f/32.png) [@Fubaya](https://boards.straightdope.com/u/Fubaya)\ **Post date:** [October 12, 2014, 3:47pm UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/17 "2014-10-12T15:47:20Z")
(Seinfield voice) If dashboard lights are so durable, why don’t they make the whole car out of dashboard lights? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 12, 2014, 3:59pm UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/18 "2014-10-12T15:59:09Z")
Not to be a wet blanket, but how durable are dashboard lights anyway? In my case, they are used maybe 4 hrs/week (if that much), so that’s only 200 hrs/year. I have Xenon Halogen lights in my kitchen that are rated for 20,000 hours, and were installed December 30, 2009. Those get at least 4 hours of use each day (that’s 7,300 hours so far). ---
**Author:** ![Smapti](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smapti/32/17938_2.png) [@Smapti](https://boards.straightdope.com/u/Smapti)\ **Post date:** [October 12, 2014, 9:29pm UTC](https://boards.straightdope.com/t/what-makes-dashboard-lights-so-durable/700936/19 "2014-10-12T21:29:27Z")
Well, they have to be reliably durable enough for you to be able to see Paradise by them, so…