This is actually a good sign - the heat is getting away from the LED and driver and out into the body where it can be lost to your hand and the atmosphere. Ithink Cree rates their LEDs to work at up to something like 90-105oC. This is the junction temperature inside the LED which is going to be hotter than the outside. I'd reckon all would be well if the head is still not too hot to hold, say 60oC or thereabouts. I'll fire up the datalogger with a thermometer and try it out.
I have this one but the dropin is a generic DX 5 mode R5 packed with foil till the dropin is difficult to remove. Ambient temperature is 19oC
The temperature sensor is taped to the light and a freshly charged 18650 stuck in it. As a result of the handling the light is warmer so I am cooling it with a fan before I switch it on. The fan will be turned off once the light is on.
Switched on at 1 minute after logging started.
At two minutes on high (1459 lux at switch-on) it has risen 2oC
After half an hour, it has not hit 40oC. Will upload a chart once I've created it. But I've just noticed the probe fell off and was measuring the air temperature around the light - the dropin bas was over 50oC. Time to try that again.
I took the temp at the triangle bit near the bottom of the head.
The battery was AW 2200 mAh. I had used it for 1/2 hour the night before, I did this test in the daytime, i could only see the hotspot and it was bright with no dimming.
The final temp was 30Min - 43.8C (110.84F). I stopped but the temp was increasing slowly.
