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.
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.
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.
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.
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.
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).
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 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.
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.
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).