I thought it did - I thought that's exactly what the 2nd chart in the OP of that thread shows? Tsp and lumens plotted?
The exact same thing applies to a computer’s CPU.
So you’re saying that in a computer environment, anything after the heatsink doesn’t matter much because the bottleneck it at the CPU to heatsink? So all those fans in the case to exhaust hot air is not needed?
*It’s all a system.
Heat transfers when there is a temperature difference. The bigger the difference, the more is transferred. *
So in a flashlight, if I can make that MCPCB cooler by 10C by using better paste, pill and body design, it will make it easier for the heat to transfer at the bottleneck.
This also explains why we need fans to cool the inside of your computer, why a flashlight can run longer at max on colder days etc.
For that analogy about case fans to be accurate, you'd have to propose some method by which the paste under the star increases the ability of the flashlight body to dump heat into the surrounding atmosphere.
I do frequently when I hike, its called rain, much cheaper than fancy paste or copper 
We’re talking about getting the heat away from the emitter.
Keeping the idea of the greater the difference in temp, the greater the temp transfer…
Let’s look at it the other way and see how the cold gets to the emitter…
The cold goes from the body, to the pill, to the paste, to the MCPCB and hits a bottleneck. But at that bottleneck, the cooler the MCPCB, the greater the difference in temp to the emitter which helps keep it cooler.
Edit: Just as the heat has to get out, the cold has to get in.
This is why every single part of the system matters.
+1
and to reply directly to your quote comfychair, the method for the body to dump more heat into the surrounding area is to increase its temperature by having a better thermal path to the emitter. This includes everything between the body and the emitter.
The hotter the body, the more heat is being dumped into the atmosphere.
I’ve read the thread up to the current post (#47), but chose to quote this one. Frankly the discussion up to this point has been more civil than I expected, but it’s still only discussion because nobody has any good data on this. I think it’s clear that both sides have good points - that’s normally where we end up having to do some testing.
One critical thing to understand about comfychair’s perspective is that he doesn’t care about die temperature unless it has an effect on light output. I do not take the same position, so my perspective on thermal matters is certainly going to be at least a little different. All other factors being equal I want die temps to go down. If nothing else it’ll improve lumen maintenance, but I think it’s fair to expect some improved performance like Tom E pointed to in pflexpro’s last graph on the wrap thread. Maybe I misunderstand something about that graph though?
In terms of the quoted post… I disagree about the density of CPU vs LED. We’re talking about ~900 square mm for a modern CPU heatspreader (1156) and running the CPU at around 60-90w (draw, not heat output) for stock speeds or the same for a mild OC. So that’s 10 square mm per watt. The back of a 16mm MCPCB is around 200 square mm and the LED is something like 10-30w (draw, not heat output). So basically the same density the way I’m figuring it. And we still see small differences even with active cooling and low temperatures. I expect to see at least small differences at higher temperatures and with passive or hand-assisted cooling as well.
comfychair also makes a good point in that the most critical joint is the one we can’t modify. The best we can do is to increase the temperature delta from the hot side to the cold side of that joint. The higher the delta, the more heat will move across it - regardless of how bad it is.
I’m not convinced that I’m right. I think it’s clear that there’s no data supporting comfychair’s claim, which doesn’t make him wrong either! Good thermal paste (not the best, just good stuff) is relatively affordable. 10g or 20g tubes of decent stuff is pretty inexpensive and you shouldn’t use much per application. So with the lack of data I just don’t have a problem covering that base. I currently use AS Ceramique because I have a ton of it, but I’ve considered switching to MX-2 because it’s easier to apply correctly and is still affordable.
BLF Rocks
We can argue till the cows come home, we need data
Anyone able and interested in doing some testing?
I was the one who brought the cpu example, just trying to prove differences when using several types of thermal compound. Not comparing their heat sinking requirements.
The key difference between effects of types of thermal compound in CPU vs effects on a LED:
In a CPU, there is noticeable performance increase even if it operates at 5C lower (for example quicker video rendering). This is why people get obsessed with the best thermal paste and even some are now using special coolants for their liquid cooling system, which is really an overkill. But because it translates to better measurable and real world use performance, it’s worth it.
In LED flashlights, you could achieve a 5C drop by holding it with your hand for a few seconds and it doesn’t come with real world use noticeable increase in output, and even if we manage to detect a few lux increase with a meter, it means nothing on real use and this level of perfection has never been applied here. So same goes for the thermal compound being used, I believe a higher grade thermal compound alone doesn’t help a light perform better on real world use. MCPCB and host plays the major role here.
I think some have turned the question from “does different quality paste affect light output?” to “do we need thermal compound at all?”. The keywords here are real world use performance and measurable performance, and they don’t always come together.
BUT…. despite everything and I know this contradicts myself: I would still choose to use a higher grade thermal paste, just because I don’t mass produce so it doesn’t mean a significant higher cost to me, also, makes me sleep better at night. It’s the just-in-case ideology.