Below is basically a copy of a PM I sent to a friend last night about the HC60……
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As far as the HC60 goes I checked it out after I saw what was being discussed on the thread.
Mine does step down after about 25 minutes on Turbo in a 75 F room with no air flow or air movement. It is really not perceivable to the eye (or at least my eye) as it does not step down a complete mode.
It just drops a few lumens and I have to be watching the beam on the ceiling to see the micro-second blink when it does it.
- First time it reduces power is two “blinks”, about 1 second apart.
- Second reduction is about 5 minutes later with 1 “blink” reduction.
- No more reductions after that.
I seriously doubt that in a cold environment, wearing it outdoors and moving; that there would be little if any reduction.
I’ll have to volunteer to go to Norway as a test dummy and learn to dog sled to verify that. 
I found the chart below done by Budda in This Review of the HC60. It is a pretty good review with some good internal pictures of the HC60.
Mine did not seem to follow the graph below however. It was much longer before it stepped down the first time.
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Testing the thermal regulation system / Nitecore HC60
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PS: If you look in the thread you will notice Budda tests more lumens that is claimed by Nitecore. This does not surprise me as Nitecore is usually pretty conservative in their published ratings it seems.