Can’t swear, but it looks to me that the HS21 uses a timer rather than temperature sensor to step down from the Turbo and some High?
no matter what the ambient temperature is, the turbo in flood mode always works for 2 minutes for me, now in winter the body is slightly warm and it still regulates down after 2 minutes of work on turbo 1200lm
1 Thank
Better properly made timed stepdown then erratic “ATR”
Probably true, but the reason for this question was that as I was switching emitters on Turbo, the light got pretty hot and then I just realised I was probably restarting the timer every time I did it.
Well, it is a down side of timed step down 
Previous Sofirn flashlights I tested said thermal regulation once temperature hits 55° C. Yet they all go passed that which is extremely hot. The HS21 manual doesn’t mention anything about thermal regulation. Looking at my runtime chart the output goes down way before it hit 55° C.
Here’s the runtime chart of the Sofirn SR12 which claims thermal regulation at 55° C. Turbo drops down quickly way before hitting that temperature and max temperature reached 58° C. Mind you I measured external temperatures so the driver temperature would’ve been higher.