What is the effect of cold temperature on flashlight performance?

This am I turned on my Klaus 900 lumen light that was in the car at 21F. It appeared to be not so bright at the max setting. Is this typical? Or should cold temperatures not have much of an effect on light output. Important, because I am often outside at night in cold temperatures.

You are likely correct in your observations. Cold temperatures increase the internal resistance of almost all common batteries, resulting in lower output to the driver/LED. On the other hand, increasing the operating temperature of the cells well above room temperature will reduce the internal resistance and allow for higher output, although it will reduce the lifetime of a rechargeable cell.

Fortunately, high powered LED flashlights are like little heat factories. As the light runs, it will start producing heat at the LED which should make its way into the body of the light and eventually to the batteries. Now, this only really comes into play if the light runs for a while. Short bursts will likely not provide the same effect.

Also note that your LED is more efficient at colder temperatures so once your batteries are warmed up, running your light in the cold is ideal.

smooth2o said:

This am I turned on my Klaus 900 lumen light that was in the car at 21F. It appeared to be not so bright at the max setting. Is this typical? Or should cold temperatures not have much of an effect on light output. Important, because I am often outside at night in cold temperatures.

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Great place you live! It must be because it STAYED in your car. I would think once it warms up it should be bright. I have used my lights in MUCH colder temps. However, the lights were inside until I used them,,,,,,,,I would think that is what the difference is.

I have used my lights in single digit temps where I live and well below Zero where you live when I was visiting and they worked fine. A few years back it was -7F and I took a 45 minute hike using my TK75vn and it worked fine! This was a few miles down the road from Art Devlins Olympic Motor Inn where I always stayed!:thumbsup: Been to WhiteFace many times with Capo my Siberian doing Triple Lundy's in the snow!!!!

You'll find that alkaline batteries are far more susceptible to the cold temps.
I've had 4D mags and 3AAA LEDs fail to function at the extreme low temps in WI, USA. (Well below 0°F).
I've found that lithium primaries seem to stave this effect off.... at least as low as -45°F which is the lowest I've used my LED car light (6AAA XP-E 3 WATT) and it was only slightly dimmer than usual room temp.... for a few mins, then functioned as a handy hand warmer! Lol
My suggestion is to use lithium in extreme cold environments.

I've mentioned this before, but I noticed my Fenix PD32UE is not any brighter on the highest mode compared to the mode below it when cold. And the interesting thing is that it is NOT DUE TO THE COLD BATTERY. I even tried a warm 18650 and the two highest modes are still the same birghtness.

markr6 said:

I've mentioned this before, but I noticed my Fenix PD32UE is not any brighter on the highest mode compared to the mode below it when cold. And the interesting thing is that it is NOT DUE TO THE COLD BATTERY. I even tried a warm 18650 and the two highest modes are still the same birghtness.

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That sounds like a defective light? Maybe? Has anyone else w/ the PD32UE mentioned that to you? I would be disappointed if any of my lights were like that.

Capolini said:

That sounds like a defective light? Maybe? Has anyone else w/ the PD32UE mentioned that to you? I would be disappointed if any of my lights were like that.

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I have two of them, so I would assume it's not a defective light. But maybe they're all like that?

Markr6, is the battery possibly not giving up enough amperage? What batteries? Fresh off the charger at what voltage?

Tried a different battery type? That is, is it same brand/model in both of those PD32UE lights?

Tried measuring the amp draw at the tailcap? Same for both modes?

Sounds more like a thermal issue with the driver. Confused over-temp safety device?

more_vampires said:

Markr6, is the battery possibly not giving up enough amperage? What batteries? Fresh off the charger at what voltage?

Tried a different battery type? That is, is it same brand/model in both of those PD32UE lights?

Tried measuring the amp draw at the tailcap? Same for both modes?

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I'll try to test it out sometime. I believe it was always EagleTac 3400 cells. I have some plain NCR18650B so I'll try those too. Warm, cold, etc.

I've read that you need a 4x increase in brightness to appear twice as bright. I've had high and medium look the same with lion before (warm or cold) and it was usually a battery not up to the drain so the high was flat.

The amperage at the tail cap should tell all. If it's the same, does it with other batteries, then it's gotta be something in the driver as Mr Fritz suggested. My two cents.