Heat management

[lightseeker2009]

Am I right if I say if a flashlight gets hotter than another, it's got better heat management? Of course if the flashlights are the same size.
Today during a loadshedding session, about 2 hours long I used 2 flashlights simultaneously as on their own on higher settings they get too hot.
So the one is a Fenix E35 V3.0. Used at its 450 lumen setting.
The other was my Folomov 26650s at its 400 lumen setting.
The Folomov is much fatter with a much bigger head and have cooling fins. The Fenix does not have cooling fins. But strangely the Folomov got about twice as hot as the Fenix, despite its cooling fins and 50 lumens lower output.
I really thought it should run cooler. It's not a issue, but I just wonder why?

 

[jtr1962]

There's so many variables that it's impossible to generalize:

1) At any given lumen output LEDs of differing efficiencies will have vastly different amounts of waste heat.
2) Some drivers are more efficient than others. More efficient drivers have less waste heat.
3) The thermal impedance of the flashlight body to ambient, along with the amount of waste heat, determines how hot the light will get.

If #1 and #2 are equal, then a flashlight with better heat management will ultimately be cooler, not hotter. However, in the short term it might heat up faster because it will conduct the waste heat to the body more efficiently. What you want to do is look at steady state. Put in a fresh battery, then let the lights run for maybe 15 minutes so temperatures stabilize. A light with better heat management will heat up faster, but stabilize at a lower temperature.

 

[turbodog]

This is a complex question and worthy of graduate level work in engineering.

You've got heat coming from:
1. The electronics. This is an overlooked area. If the circuit design is poor, significant heat can be produced here.
2. The led itself. Again, good led selection can have significant effect on heat produced.
3. The batteries... they don't make a lot, but it's still a factor.
4. The optics. Leds don't produce a lot of IR (like incans) but it's still there. If the optics (reflector, lens) are trapping this... then it can produce heat.
5. The mass of the light.
6. Thermal path from the heat sources to the air/user's hand.

 

[alpg88]

Often lights have drivers that are also heatsinked, so it is not just the led that heats up the body, but a driver too. sometimes it makes quite a bit of heat, I try to heatsink all drivers when I build my flashlights, since I do not build classic shape lights, my led and drivers are in separate areas, and have separate heatsinks, some driver's heatsinks heat up too hot to touch. other drivers do not heat up much at all.

 

[lightseeker2009]

The Fenix must then have a more efficient driver.
Fenix claimed runtime at 450 lumens is 7 hours, Folomov claims the same runtime at 400 lumens, both have 5000mah batteries.

 

[turbodog]

The Fenix must then have a more efficient driver.
Fenix claimed runtime at 450 lumens is 7 hours, Folomov claims the same runtime at 400 lumens, both have 5000mah batteries.

With everyone focused on output... efficiency probably takes 2nd place.

450 is enough get a light toasty fairly quickly.