That brings up the point of whether it *really* matters or not. I've been using my TK40 for about five months now and not once have I ever thought, "gee I wish that this was brighter" during use. So, whether it actually puts out 630 lumens as stated boldly by Fenix or 550 lumens as measured by Bigchelis last week, does it really matter in real world use? To me, not really because the light works very well for my personal use. In an ideal world, the flashlight manufacturers would have an independent certified lab do all their light output measurements. That seems to be an impossibility though.
Thank you Bigchelis for being a warm host last week. Your tests are a *HUGE* eye opener for me in terms of how much these manufacturers over-hype their light specs. They really should get their act in gear.
Also, on the subject of Arctic Silver 5, I bought a tube of it for my 4D cell Maglite with the Terralux TLE-300M-EX that you tested. Without the thermal compound, the body of the light did not get warm at all when using it on high mode. With it, the body does get quite warm after a few minutes of use, so it does work and work well at dissipating heat. The tests that you did last week were with the Arctic Silver 5.
I bought the same size tube that you did but I got mine at Radio Shack. It also was $9.50: