LED Dashboard Backlights - Dimming Works!

[Oubadah]

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[Alaric Darconville]

Here's my WAG: The dimmer reduces the current going to the LEDs.
(Imagine that!)

 

[Oubadah]

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[Kuryakin]

A lot of cars have been using PWM dimming for quite some time, my 1987 Subaru (long gone) had it.

I've just replaced my 1995 Jaguar's incandescent dashboard backlights with LEDs, and I was assuming that I would be forfeiting the Jag's dimming control.

But lo and behold, the dimming works fine! How is this possible?

 

[Oubadah]

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[Kuryakin]

No, they can also dim with a rheostat. However, since they draw so much less current than the standard incandescent dash lamps, the stock rheostat may not do much for these.

PWM simply means the dimming controller doesn't care about the size of the load, as long as it doesn't overload the unit. PWM essentially provides voltage control, and rheostats provide current control, albeit a somewhat oversimplified explanation!

Given that plug and play LED lamps for this sort of application have the resistor already built in, voltage control works fine.

So is it correct that LEDs only dim with PWM?

 

[Alaric Darconville]

Everyone told me that dimming would no longer work if I installed LED. I thought they needed special PWM dimming or something.

Is it OK for the car to dim them? Will it cause any damage, or shorten the lives of the LEDs?

Everyone told you wrong, I suppose.

No, no damage will be caused. Damage to LEDs doesn't work that way.

 

[Lynx_Arc]

If your LED dropins only have a resistor in them (no buck circuit or linear regulator) then it should just depend on the range of the dimmer circuit. I would guess most older cars just have a variable resistor and it should work fine if the range doesn't ramp up too slow or fast making it dim very little or just seem to go on/off.