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I was idly sat waiting at the lights with the indicator flashing away and tried to remember the last time an indicator bulb blew. I have never had one go was the answer, numerous Volvos have blown all the others and headlight bulbs seem to go every now and then on other makes but why this immunity for indicators? on the face of it they should be the most vulunerable.
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Surely because they are only intermitant and momentarily illuminated for a short time compared with other bulbs. And the fact many people don't use them ;-)
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I have had indicator bulbs fail from time to time, but nowhere near as frequently as headlights.
I believe the usual failure method for bulbs is thermal shock, as the cold resistance is a fraction of the hot resistance - resulting in large surge currents as they turn on, and the consequent fast increase in temperature.
Modern electronic flashers possibly reduce this surge current - ramping the current up over 10mSec will do the trick. Certainly, indicator bulbs will stay warm during the 'off' flash.
Ian.
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I actually had to replace two on a BMW - believe it or not !
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From my days in the car spares game, the bulb we sold most of was the No 380 twin filament 21/5W brake/tail lamp bulb, and it was nearly always the 21W stop lamp filament that had blown.
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In order to provide the lamp failure function required by Construction & Use Regulations, the flasher unit has to measure the lamp current. This involves the fitting of a small shunt inside the flasher which also reduces the voltage available to the lamps.
It's not a lot, but the curve showing lamp life against applied voltage is very steep - about a cube law I think. Consequently, a small reduction in lamp voltage gives a marked improvement in life.
More generally, French cars tend to have their voltage regulators set very high. This has a detrimental effect on lamp life generally - but the incandescent headlamps are correspondingly quite good as a result.
659.
Edited by 659FBE on 06/09/2009 at 19:15
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>I believe the usual failure method for bulbs is thermal shock,
Many years ago I worked on process control equipment in Namibia. Some of the older control panels still used pygmy lamp indicators instead of LEDs and the failure rate was astronomical. I had one panel with over 300 lamps modified so that all lamps were given a constant feed to keep the filaments glowing slightly. Failure rate dropped to near zero.
>I actually had to replace two on a BMW - believe it or not !
It was probably shock PU. They weren't expecting it.
Kevin...
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In 20 years of driving (x2 - me and swmbo) we've never lost an indicator bulb to broken filament. In fact the only reason for replacement has been the yellow coating on the bulb itself disappearing - twice. An MOT fail for showing a white light.
Steve
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I've lost count of the number of cars I've seen with just one indicator franticaly flashing.
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I've lost count of the number of cars I've seen with just one indicator franticaly flashing.
Must be an intermittent fault.
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