My 1st job was at a machine shop, I worked on a metal lathe from time to time. The first time I worked on a metal lathe there was machining steel. While doing so, the material that was being removed would come off in long, thin strips, and they were so hot they turned blue. If it touched your skin it burned badly! Even after sitting on the floor for a few minutes, it could still burn you. But then I worked with aluminum, and saw that it loses its heat from the friction of machining almost immediately. its turnings were short and thin. Didnt turn blue either like steel did. It dissipates heat much, much faster than steel(or most other metals). You could pick it up or touch it within seconds of it being turned off the lathe and it would already have cooled down to room temp.
I rarely ever use turbo or high settings on my lights. I'll turn it on to show people or just to check it out myself here and there, but within seconds I turn it back to low or medium, which with most lights I own, thats all I need.
But I just read that you shouldnt store extra Li Ion batteries fully charged to the max voltage. I dont yet have a Li Ion charger that will discharge, so I took the 2 spare 18650's I had in storage at full capacity and full voltage and put them into 2 lights to run them down a little. I used my Eagletac G25C2, and my Sunwayman T20CS. These 2 lights both run on 1 - 18650, and both have XM-L U2 LED's. They have very similar sized reflectors, so their beams are almost identical.
The ET G25C2 is thicker in most areas, and has 5 shallow, thin fins around part of the head. The SWM T20CS is 1/2" shorter, and is thinner in the battery tube, and has these artsy side fins on the head, but they are small and dont circle the entire head.
So I turn them both on turbo, which is about the same brightness on both lights, and I let them sit there. I check them every 3 minutes or so. The SWM starts to heat up in 1-2 minutes, but the ET is still below room temp for 3 minutes. Eventually after 25 minutes, the ET is about 95 degrees F, and the SWM is so hot you can only hold the head for about 7 seconds before it feels uncomfortable. Its about probably 130-140 degrees at least. It was still getting hotter, whereas the ET had stabilized at its temp and wasnt getting hotter from 15 minutes onward.
I think the reason for this discrepancy, is that the ET has a much thicker mid section, and since heat travels so fast and so well through aluminum, I think the thicker mid section of the ET plays a role in providing more aluminum for the heat to move through, and the fins probably play a significant role too, but they arent deep, and they only cover about 1/2 the total area of the head. Aside from that, the heads on both lights are about the same size, with the ET being a bit thicker., and the SWM's fins being less prominent.
Aside from those 2 possibilities, I cant completely figure out why there would be such a big difference in the heat retention of these 2 very similar lights....... Maybe the SWM uses more current? Who knows........
Have you noticed that some of your lights get much hotter than other, similar lights?