The biggest limiter on sustained brightness seems to be heat. You need to keep the batteries and the operator’s hand from getting too hot or else you can have an uncomfortable or even dangerous situation.
I assume the driver electronics probably can’t get too hot either, but what about the emitters?
Can’t some LEDs run at 150C or at least 100C?
Could you have a light that has the batteries (and driver?) thermally insulated from the emitters so you could just let them run hot? Maybe put a heat shield around the head, like on a gun barrel, to prevent burns.
Some headlamps have a remote battery pack and are often already insulated from your head with the holder, so they might be able to get away with more liberal temperature limits.
LEDs are just semi-conductors, they have temperature limits and degrade faster at higher temps. The phosphor coatings also don’t like high temps. For passive cooling you need thermal mass - if you isolate the grip/battery compartment you will have to put extra mass on the flashlight head, making it heavier and more unwieldy.
Further to Valynor’s response. The critical temperature is the junction temperature, some LEDs are indeed rated for 150C, (eg. XHP70.3).
The junction temperature will be the hottest part of the light, heat will “flow” from high to low temperature.
Once thermal resistances are taken into account (MPCB, interface between MPCB and the shelf, etc) the external temperature of the light will be much lower despite the junction temperature reaching 150C. Most lights use the driver to sense temperature, there will be a significant difference between the temperature the driver “sees” and the temperature of the LED.
IIRC, There were some LED4POWER MPCBs which had thermal sensors directly on the LED MPCB so that you could run closer to the limit.
Just my view of course: I’d rather avoid the heat. The heat to me is an indicator that my led is using lots of energy for heat rather than light. I run whatever mode is sustainable as the max. If I wanted more light I’d just get something with an sbt90.2 for example. Do it easy at a mid range with lots of reliability, tolerance and battery range vs something highly strung running beyond it’s limit
Before I found this site I rigged a cheap plastic amazon AA headlamp to run off a couple 18650s in parallel in a battery holder in my pocket. When I went to take the headlamp off after a few hours the headlamp had melted. Never noticed. All the LEDs still worked but the plastic lenses and all the plastic around the LEDs had melted away from them
Heat kills solid-state electronics. At some temperature or after being cooked at a threshold temperature for so many hours things start to fail - LEDs, transistors, coils, resistors, chips, capacitors. Especially electrolytic caps which I gather that even at their highest grade I are more heat-sensitive than LEDs and there’s no substitute that offers comparable capacitance density at a similar price.
While one can determine the weakest component in the design and set the ultimate power limit so as to prevent (or at least limit) its degradation or failure, one suspects that by the time the light gets hot said components are already in their danger zone thus further ramp-down is needed to prevent damage.
And as others have stated - you’re probably well into diminishing returns on output by the time the light is unpleasantly hot.
Presumably the designers have a solid understanding of sum of the thermal resistance on the path between the LEDs and the sensor and program the driver to behave accordingly.
Yes, somewhere in the 1000 pages of legal jargon it probably says it order to achieve the 50000 hours lifespan of an LED you need to keep it below a certain temperature.
Haha! Reminds me of the time I wanted to test some off road lights for my truck, so I wired 3 18650 cells in series to get around 12 volts. I hooked them up directly to the light, which glowed brightly for about 5 seconds before going out. I don’t know how much current it pulled, but all 3 of those batteries were too hot to touch for the next several hours, and never recharged again
I remember the Van 't Hoff equation - Wikipedia from chemistry lessons in school.
In short: for every +10K the speed of a chemical reaction grows by a factor of 2x-4x.
The aging e.g. of the phosphor coating is just a chemical reaction, too. Lower temps are much better.
Convoy S2+ with copper pill sustains turbo better than unihead lights, be it alu or copper ones.
The reason for that is that there’s good thermal conductivity close to the LED and worse farther from it, with a small thermal barrier in the form of threads.
This way the LED runs hotter than it would in a unihead light…but it improves turbo times.
The general principle is that introducing well designed thermal barriers improves turbo times. It may or may not impair sustained performance.
Some time ago I contemplated the use of deep fins with some thermal insulator at the very top. The hotter surfaces near the bottom of the fins as well as overall large radiating area would more than compensate for the cooling losses of the added insulators, possibly improving the light’s ability to dissipate power.
I haven’t seen that implemented in practice though, so maybe it’s not as good as it seems to me…but likely it’s just more hassle for the manufacturer than it’s worth.
Plus disable thermal protection at software level and turbo perfomance will be better… for some time Whats how all cheap trash 10000000lumen lights works
Whats how all cheap trash 10000000lumen lights works