Well if you were simply Not given the turbo option (so you only have low and maybe up to a ‘medium’) then you would not have any thermal issues to complain about. I guess that be a preferred option?
A small light with a turbo output is fundamentally a short term situation due to thermal limitations. Its physics that cannot be avoided with the current efficiency of emitters/drivers and the size of your torch.
With a XM-L driven to full 3A for example, you have a huge amount of heat bring produced. The primary goal is to keep the LED within operating range. up to 80 degrees? ©
There are 2 ways of doing this.
1) Thermal DISSIPATION - removing the energy to the external environment - I.E. heatsink AREA. A large surface area, and airflow over this area helps to remove this heat energy to the air. You need a large area to effectively keep the LED within operating temperature.
Using this calculator, Assuming a plate area of 50square cm (the surface area of your pocket rocket XM-L torch), and airflow rate of 1m/s (walking around). Lets also name 60 DegC as the hand scorching temperature.
http://www.efunda.com/formulae/heat_transfer/convection_forced/calc_lamflow_isothermalplate.cfm#calc
A 50square cm plate, with 1m/s air flow over the plate, for a plate at 60 Deg C, ambient 25 deg C, is able to dissipate around 3Watts of heat.
If your XM-L is generating 10W of heat on turbo, your LED generates much more heat than 3W, so temperature will continue to rise beyond hand scorching temperatures (about 60 deg?)
Using the calculator again, at around 130 degC, the 50 square cm plate will finally be able to Continuously dissipate your 10 watts of heat. So its therefore quite obvious that your small pocket rocket has no chance of keeping up with a fully driven XM-L from a thermal dissipation point of view without getting to ridiculous temperatures.
If we however increased the plate size to 200 square cm, (10x20cm plate) which is closer to that of a large 3x18650 torch body), it can comfortably dissipate well over 10 watts, and stay below 60 degrees.
SO what else is there for our little pocket rocket….
2) Thermal MASS - the mass of the heatSink absorbs the thermal energy. So the larger the thermal mass, the longer it takes to warm up the torch. (like putting more water in your kettle, means it takes longer to reach boiling point for a given energy input)
Your pocket rocket is a small device again. Lets say it has an effective thermal mass of 50 grams? Lets be generous and say its 100 grams of material that you can heat up (thermal resistance not included). For a 10 watt heat source running for 1 hour, your 100 gram aluminium body will increase in temperature by around 400 degrees C.
Thats a little warm! If we divided that down to 5 minutes, thats a 30 degree rise. So if we start at 25 degrees, we will end up with a 55 degree torch in 5 minutes. Realistically most of the torch doesnt actually get heated up, the battery tube is connected with grease through a thin threaded section, the battery is not really connected thermally to the LED at all, and remember that your driver board also puts out heat too!.
A 500 gram thermal mass however with a 10W heat source for 1 hour will only rise 80 degrees. SO even with NO heat dissipation, by 1 hours time it will only rise 80 degrees. And as we have shown above, with sufficient surface area, it is well and truly able to continuously dissipate heat anyway.
So physics is at play here, there are no 2 ways around pocket rockets and heat. We have demonstrated that its too small to continiously dissipate heat, and too small to absorb the heat without getting crazy hot, and rapidly. The only way is to Reduce the heat being generated (turn the output right down (medium mode?)), or use more efficient emitters (every new emitter released is improving on this), or increasing the rate of cooling (airflow, surface area).
In conclusion, I agree that many compact lights have a turbo mode, and it would be nice to expect to be able to utilise the full runtime quoted on turbo in one hit. A light that is able to deliver turbo continiously is indeed a better light, however you must understand whats happening to allow for reasonable expectations.
With a physically small torch, using current LEDs the manufacturer can offer up to 200 lumens safely, but the consumer wants more, so turbo is offered to you with a caveat of short term operation, which is limited by the physics of thermal management of a static aluminium tube as demonstrated above.
Your hot rod ferrari overheats too, if you dis-respect its operating conditions. If you constantly sit on the red-line and your not moving (airflow for cooling) you can expect it to overheat. A ferrari was designed to race though, so it can rev away if your on the track for hours. Certainly on the limit though.
How about a smaller car, a daily drive, 1.3L 4 cylinder, with the small air intake and small radiator. Designed to run at cruising RPMs, and has a little thermal capacity to handle the occasional hard acceleration. If you were to drive it like you stole it all the time, and sat on the red-line 7000rpm all the way to and from work for a long continuous drive, (and kept it on redline at red lights), you can be sure that its not healthy, and thermally not able to handle this more than a few minutes. If you then went to the manufacturer and complained that the car overheats every day after X minutes of red-lining while parked, Im sure you wont get a happy reply.
My 2 cents, and hour of sitting infront of my computer