Question about over driven led flashlights...

From what I understand, overdriven leds in flashlights are ovedriven as a result of not being regulated. To me, it would make sense to use NiMH batteries in this type of light since they are only 1.2v to start with so there would be less voltage applied in the first place which should make the LEDs last longer in the long run. Is this correct?

One of my LED lights (Coast Tac Torch v2 6 chip dual color) is powered by 3 AAA batts and I plan on using NiMH batteries only in it so as not to overdrive the LEDs as much as they would be by fresh alkalines initially. Is my thinking on this correct here or not?

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Nimh batteries are not exactly 1.2v, but under moderately heavy load they tend to not sag much below that. Off the charger a nimh cell can reach voltages over 1.4v at times. I think the standard operating range is more like 1.2-1.35v. Depending on the Vf (forward voltage) of your LEDs you may end up overdriving them some anyway, but most semi decent 5mm LEDs can take a minimum amount of overdrive without frying. I tend to not try to overdrive them any harder than 40ma using fresh alkalines so nimh will overdrive them even less than that. I have a cheap 8 LED light using 3nimh and it has burned out several of the cheap LEDs in it already but I estimate it is running them at 45-55ma.

Many lights are resistored so that the leds will be overdriven during the early peak output of alkaline batteries. After the alkalines decline in voltage to a stable mid-range, the leds will usually not then be overdriven. And as the batteries go into decline, this resistoring setup will allow the leds to put out a still useful amount of light.

If the leds were set so that they ran at 30ma on fresh alkalines, the light output would decline quickly and be very dissappointing for most of the life of a set of alkaline batteries. Some overdriving in the early part of the alkaline cycle probably doesn't cause too much harm- especially as the actually lifetime hours of usage of most flashlights is a lot less than the rated life of the leds....probably like 30-100 hours in the life of the average flashlight.

Current regulation will keep the led at a constant level of brightness thru most of the battery lifetime. However, the regulator circuit can be set so that the led is overdriven at a constant level. So regulation is meant to produce a constant or more consistent light output and is not necessarily associated with driving the leds at spec.