Curious:
Q1: Are there thermal issues for the 18650 itself or is this just about the emitter getting too hot ?
Q2: If heat dissipation is a size limiting factor, what then is the smallest 18650 light that could "continuously" run eg: a Cree 100 Lumen/Watt light continuously as 1000 Lumen == 10W heat dissipation, flashlight body staying below 50 C at ambient temperature of 25 C ;-) ... Or is that the wrong question and the best trick to dissipate the heat is to keep the flashlight head thermally insulated from the body and give it all the work to dissipate the heat (don't touch the head during operation...).
Q3: If heat dissipation is the issue, would investment into copper help ? Any flashlights with out there ?
Q1- Basically the LED's are putting out very high outputs, these are too high to run in single 18650 form/size/mass/heat sink.
Q2-The Emisar head does get too hot to actually touch and the body very warm. Not a flashlight for kids or people who dont have an interest in lights IMO. Along with size/heat sinking, its important to get the heat out to the body to help dissipate...... The hand holding the light helps this, over say being left tail stood on the side.
Q3- Cu does help soak up the heat,but also can get very hot depending on the light. Cu is great in fact, however it is also dense/heavy/soft. So using cu inside the head as added heat sink, or actual cu heads(the s41 to name one flashlight, cu cryos head to name a custom part . Texas Lumens makes some very nice hosts that are cu, although the weight is not always ideal for EDC, cu does get a nice patina and for me gives it a personality.
50oC with ambient 25oC with most 18650 lights, you would struggle to hold much over 600lm/type output. There are many more factors of course, so only rough! Depending on the LED itself (look how hot an xhp 35 and xhp 70 run!!! ).
If 1000lm is needed(also bare in mind a single 18650 light even holding that output would not get you through a night), then a dual 18650 light would be better for heat management(general comment with added size/heat sink)along with running time at that output. To get hours of 1000lm use for around 4hrs(variable, just rough example) then a 4 cell light would be required .
Basically, a single 18650 lights use of around 1000lm is usually a burst or turbo mode, 3-5mins it will step down or become too warm/hot. Depending on your actual requirements te36 would depend on which light would be more suited for you. High output/run time and heat management usually means going up in size from a single 18650 light. A 600lm thrower light will throw light a lot further than a 3000lm flood light. So over actual lumens, i tend to focus on what actual type of light for a specific application. Some want to throw a light to spot things in the distance, they down want to flood a field to see that object 300yrd away. Just an example..............