# The life of auto dash lights?



## Orion (May 5, 2003)

I was told (by the dealer) that my dash lights will last the same amount of time regardless if they are on full brightness or if they are dimmed.

My question is, . . . is this a true statement? I would think that dimming the lights would cause them to last longer because not as much current is going to them, thus they aren't running as hot, thus they shouldn't burn out as quickly as running them at full brightness. 

Can someone /ubbthreads/images/graemlins/help.gif?


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## Saaby (May 5, 2003)

It's the thermo cycling that really kills them, so if you want them to last a real long time either always leave them on (Even when the car is on) or always leave them off /ubbthreads/images/graemlins/wink.gif



I think it's 6s really. Some will argue, as you have, that they won't run as hot and the thermocycling won't be as dramatic. Others will argue that running them dim will cause them to burn out EARLIER since they aern't really designed to be dimmed. 

If you really want to extend the life of your dashlights leave your headlights off in the day, or if you've got a car like my [sister's] Volvo that has DRLs (Lights run all the time) at least turn the dashlights off durring the day. Also, you might, at night, instead of just turning on your dash lights dim them all the way, turn them on, and then bring them up gently from dim to full brightness.

Even if they're a pain to change (sometimes) bulbs are relatively cheap and, if youre up to it, usually user replacable.

What kind of car we talking here?


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## Orion (May 5, 2003)

It is a 1997 Hyundai Sonata, and I've been told that the cost of replacement is rather high, most of it being the labor of removing the dashboard. If that happened, I'd rather get an LED replacement for all the bulbs in there. But that's another topic. This one is to determine if it DOESN'T matter if you have them at their fullest brightness, or constantly at a dimmer setting, which is where I leave them all the time.


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## Zelandeth (May 5, 2003)

I wouldn't panic yet, Our neighbour's got a '87 Volvo 260 (I think), and thus far, the only light to have failed is the one in the clock...In my current car ('88 Renault 11TC), the only bulbs to have gone are those in the heater controls, and the rear foglight switch. If you wanted to eliminate thw worry factor, I'd suggest spending a bit extra on an LED conversion.


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## Evan (May 5, 2003)

I agree with the dealer, backing off the brightness a little will increase the life. Remember those 100-year night-lights that are just 2 bulbs in series? I think only halogen bulbs are harmed by running them too cool, but then my car has always-on halogen headlights that are just slightly dimmed if I havn't actually turned them "on".

Replacing dash lights can be a real pain. I had my last VW about 13 years and I think the dash light died at about the 8th year. When I went to replace it, all the plastic behind the dash had gone brittle, so the odometer cable snapped. In my current VW I keep the dash lights just a little short of full-on and hope they'll last as long as the car.

On the other hand, most people don't keep a car 8 years, so why worry?


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## EMPOWERTORCH (May 6, 2003)

I seem to recall that VW were using LED's in thier dashboards at one time, although I think the dial lights may still be filament bulbs, all tha annunciators were 5mm LED's. The mid Eighties Polos and Golfs all had LED's in the dash.


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## Willmore (May 7, 2003)

Evan is dead on WRT the 'dim only kills halogens'.

For normal incandescants, there are three main ways to die: inrish current, mechanical failure due to thermal cycling, and erosion of fillament due to high temp/time.

Inrush is when the lamp first turns on. A cold filament is several times more conductive than a hot one and the current through it for a given voltage (given a constant voltage supply which a car battery sure looks like from the standpoint of a little dash incandescant) is that many times higher, so it pops like a fuse on a bad ckt. Put a little brains into a dimmer/soft startup ckt and this goes away completely--as seen in high end cars for the last few decades.

Thermal cycling. Can't beat this one. Lamp gets hot, lamp gets cold, lamp gets hot, lamp gets cold... repeat a few thousand times and little bits of metal and glass get cracks in them and they break--or the metal dies like above.

Erosion. This is the best case cause of death for a lamp. /ubbthreads/images/graemlins/smile.gif It's somewhat inevetable, but highly controlable. The life of a lamp varries with some high power of the voltage through it. Find exact info on Don's web site. Basically, electrical and thermal effects play off eachother as the bulb gets hotter and thing go bad very quickly as voltage goes up. So, set the dimmer to 80% or 90% and the bulb lasts for decades.

There is one other way that incandescents die that is common, but not really applicable here. It's due to vibration fatigueing the metal in the fillament. You don't tend to see that in cars, but you do see it in tanks, helecoptors, and air planes. They solve it by keeping the bulb on. They just go from 10% brightness (off) to 90% (on) and the difference in brightness is enough for people to detect as off and on. The fillament doesn't fatigue as it's *warm* all of the time and that's enough for the atoms to no do that fatigue thingey. Yes, one time where thermal effects are *good*. /ubbthreads/images/graemlins/smile.gif

Halogens are a completely different animal and I won't even get into them.

I've got LEDs for allmost all of the interior lights of my car--dash, radio, accessories. The only incandescents are in the vanity, the map light, and in the 'curtesy' lights. Those get so little use that I have no real worry that they'll die.

Oh, EmpowerT is a little off. VW was the first to use a blue LED as a high beam on indicator. I think that's the only LED 'first' they're associated with. A SiC blue LED looks a lot like an incandescent bulb with a blue filter and many people didn't realize that's not what VW was using. /ubbthreads/images/graemlins/smile.gif But, using LEDs for all dash lighting? No, they were late to the game on that--as far as European cars go. They're miles ahead of American cars, though. *hangs head in shame*


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## NightShift (May 9, 2003)

Ok, so then how long does electroluminescent cluster lighting last?


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