My prediction was based on my experience with thermal compound used mounting heatsinks to cpus. I’ve tried both spreading a thin layer using a plastic card (credit card, id, driver’s license, etc) and the ‘grain of rice’ method and found that there was little difference in the effectiveness even with heavily overclocked multi-core processors. This goes back to the days of good old 400MHz celerons oc’d over 1GHz on a dual processor board to more recent and more modestly oc’d core processors like a core 2 duo rated for 2.4GHz at 3.6Ghz. Using the same compound and heatsink the cpu temp was within a few tenths of a degree under heavy load (running a boinc app on all cores).
It’s likely that in the case of cpu heat sink and thermal pad assembly the manufacturers are a bit more diligent about surface prep than the run of the mill light manufacturer. I daresay that a similarly poor standard of prep would result in more than a few tenths difference, especially if no thermal compound were used or so much that a bad fit was not apparent(both of which are common enough with lights). Granted, the majority of flashlights don’t push the limits nearly as far but it’s just common sense to increase the scrutiny as you increase the power.
Not entirely surprising, keep in mind, we only see up to a 5-10c difference between best and worst with computer heatsink pasting, and that’s pushing up to 600 watts of heat through a 2x2 inch square.
It’s never a bad idea to do it the best possible way, especially when it’s cheaper and faster though.
since the hot spot is the center of the mcpcb the dot in the center is best.
you want just enough to spread well but not make a mess or waste compound.putting the dot dead center ensures there is enough in the critical spot.
if you do that any differences are so far “down in the noise” that its not worth worrying about.
making sure the surfaces are flat goes further than obsessing on compound anyway.
And now a third test
This time,
Check with a new razor blade if the surfaces are flat, if not, no test dab thermal grease as you like you’re done 
If flat use a very little paste on both surfaces but spread it and then swipe with something flat (like that new razor blade slightly tilted away from cutting edge (so pull backwards so to say)) and get rid of all paste except the little bit that is filling the gaps it is supposed to fill (this is mentioned before in this topic)
This should be the best methods for it is only there where needed, I dislike the dab-push methods a lot for less is more and the obky way to be sure allnis covered is if it bulges out the sides, so one always have to use too much.
On CPUs using a credit card or something and spread so fine that the markings on the CPU can be seen then cooler pressed down with some wiggle before tightening is the best way to go and very easy, half a grain of rice sized for those large CPUs and a led star is much smaller.
It’s pretty bad when I’m spreading cream cheese on a bagel at work this morning and started thinking that it looks like thermal compound filling in all the holes and crevices! Too much cream cheese is not bad in this situation.
Please see my Thermal Compound – Another Experiment post for another experiment I performed comparing no thermal compound versus using thermal compound. I think applying thermal compound is beneficial for any flashlight and is critical for higher powered flashlights.
I think I’m done with my testing. It seems to me that there would only be an issue in a flashlight if no thermal compound was used or if too much remained between the surfaces.
Reviving a topic but will Thermal compound like Cooler Master MasterGel Pro CPU Thermal Compound work? I’m trying to find the right stuff in SA but it’s not that easy check their specs please for me http://www.coolermaster.com/cooling/thermal-compound/mastergel-pro/
Honestly for flashlight usage the thermal paste you use really doesn’t matter that much. As I showed in some tested I did with proper clamping force even no thermal paste at all preformed within a few lumens.
The thermal paste just makes it a lot easier to get the best results.
I generally just use whatever I have laying around, the white silicone based paste works fine for most things.
I have switched from that to AC5 when testing LED’s before and saw virtually no difference in the results.
Even on computer CPU’s thermal pastes generally only change the temps by a few degrees.
Thanks TA appreciate the info