LED lit gauges, North Hollywood vs bulbs Options

[Grngoat]

Does anyone have any experience with the LED lighting that North Hollywood Speedometer does? Especially, how does it compare to just buying the LED bulbs that are avaliable as replacements?

The price that they charge to convert the gauges is quite a bit more than just buying the bulbs. I'm just wondering if they do that much better of a job or not.

Anyone?

[davesprinkle]

QUOTE

Several people swear up and down LEDs are dimmable w/o a "controller" (basically a PWM circuit).  I'm not a EE, and I've not fooled around with LEDs enough to know for certain, but this MAY be true, even though it goes against what little electrical theory I know.

If you don't mind, as an EE, I'll weigh in here... Here's the deal with LEDs -- somewhat simply, an LED's light output scales with the current that passes through it -- more current = more light. So far, pretty simple. The complexity comes in the exponential current to voltage curve of an LED, which effectively means that if you apply more than about 1.5 to 3 volts (the exact value varies), then you start to reach the "vertical" section of the curve, current starts to go to infinity, and the LED turns into a DED (Dark-Emitting Diode).

So, getting to the point, to run an LED properly, you need to be able to precisely control the current passing through it. At its simplest, this can be done by just putting a resistor in series with your LED and the 13.5V charging system in your car. You would choose the value of the resistor so that the current passing through the diode would give you the brightness you need.

You could dim the LED in a couple of ways:
1. By replacing your fixed-value resistor with a rheostat or potentiometer.
2. By using the fixed resistor and by switching the 13.5V power supply on and off. During the "on" times, the LED's brightness would be determined by the current established by the resistor. And during the "off" times, the brightness would be zero. Don't want your dash lights to flicker? Well, just increase the switching frequency. At some point, say about 100Hz (100 cycles per second) or so, human beings cannot detect any flicker. The bright "on" times sorta blend in with the dark "off" times, and the perceived result is somewhere in the middle between the two extremes. Exactly WHERE in the middle is determined by the time-ratio of ON vs. OFF. Want 99% brightness? On-time of 9.9ms, off-time of 0.1ms. Want 50% brightness? On-time of 5.0ms, off-time of 5.0ms. Etc. Pretty straightforward.

I think the more significant question is: WHY?
LEDs have only 1 advantage in this application -- they might last longer. (And even that isn't a sure thing -- to get the longevity, you'll need to keep your current low.) I'm not sure that advantage is worth the additional cost and less-pleasing light.