No question there. The TK75 is an awesome light. Fenix did their homework on this one.
Thanks for the wicked detailed trial run on these lights 
Did you take any temp readings of the emitters? That + external temps reveal a lot about overall heatsinking effectiveness.
What a great testing pal.
I believe both lights are winners. I think we won’t go wrong with both
Yup im Adding U3’s asap .
I didn’t do any at the emitters. Didn’t know if I could do that. Will these infrared guns work through the glass?
I’ll likely leave my U2’s in there for now. If I upgrade, it will be a ways down the road and likely XM-L2’s.
I would like to do a UCL or AR lens swap. It was suppose to have that from the factory anyway.
IR temp guns do not work through glass.
Thanks for the testing.
It looks like the BTU could use a little better thermal coupling to get the heat away from the emitters. A 400 lm drop is significant IMHO.
I’m thinking of doing 3x XM-L2 U2 on copper SinkPads in the future.
The IR temp gun thing is new for me. Never used them before and just got this one Saturday. Wanted to play it safe just in case one of the lights started getting very hot. Both did ok I think on temps. But yeah, looks like the TK does a better job of getting the heat away from the emitters. A 395L drop for the BTU vs 225L drop for the TK75. I still wonder if the drop was partially due to the driver trying to bring it down slowly to high. I think the drop figures about a 13.7% drop on the BTU and about 7.6% drop for the TK. The TK did very well for sure.
But I’m not too worried about it. I never intended to use the light for 20-30 min. anyway. I got it for fun. And if I want to use it for extended periods, I’ll just let it go naturally into a 2000L high and leave there. But I know now I can run it on turbo longer if needed.
Swap in XM-L2’s on copper sinkpads, along with a UCL - the BTU would be even more beastly then.
I had XM-L2 U2’s installed… Had some resistor work done. It’s just under 4a on turbo… Really happy with it. ( btu )
Thank you rdrfronty for testing them out.
Your TK75 result match with runtime chart I have seen that output drop about 5% in 20 minutes Turbo mode. That is very good performance I would say.
No comment from me for BTU.
I confirmed from preliminary testing that the driver current does drop during the first minute or so. It started out at 3.7A and dropped to 3.5A rather quickly (emitter current). Nothing huge, but it should contribute a bit to the fallout. I’ll be tweaking my output a bit to compensate, shooting for 3.8-4A on turbo.
Once I move to XM-L2 U2 on copper, I might bump it up closer to 4.5A (depends on output curves from XM-L2 when they are done). This driver seems to be comfortable with high current output.
Thank you for the performance analysis and the temperature / lumens statistics.
Was really looking forward to your report.
Now, for a ton of light and extended use, the BTU is good with a conservative 10 to 15 mins on turbo and the rest on high. This is a 2000 + lumens light all the way until battery failure. Now, with a little tinkering, the BTU is set up for an even greater performance and greatness.
In the flashlight universe, rarely does a torch delivers both - massive throw and flood of over 2000 lumens all the way. The BTU is a truly living testament to all discerning owners and lovers of led flashlights.
Great job RDR. I am certainly impressed.
That slight current drop is good to know. Thanks for that little detail. So perhaps the light loses maybe 200 lumens or so due to heat and 200 lumens due to driver output dropping slightly.
I think a 200mA reduction across three LEDs would be quite close to 150-200 OTF lumens of loss (around 50 or so per emitter). The rest is likely heat sag. Since the driver sage is quite quick, one could compensate by jumping up to 4A drive, which would fall back to 3.8A within a minute.
so we all agree Ric Awes us a nice coated lens ??
I’ve been hunting around for one without much luck yet. Found one company, but they have a minimum of 25.
It would be nice of Ric would upgrade us, but I’m not going to dwell on it.
[quote=Shaquille]
My U3 has been shipped by fasttech and my soldering iron is all sharpened up tinned and ready muahahahaha
I strongly suggest to stop using that fujic crap .scrap it out and use a thin coat of "silver thermal compound" or artic silver and similar cpu products .It will greatly increase heat transfer from the emmiter
so heres my upgrade FOR MY BTU asap to beat the tk75 now
1- change over to U3 for higher lumens----AVAILABLE-
2- Remove all cheap fujic crap and use expensive silver thermal compound for better heat Transfer. ---AVAILABLE
3- change lens to ar coated lens -? ----NOT AVAILABLE--cant find ...hoping Ric has answer to this
This has been and informative and very excellent thread. Thanks to all participants. Both of these lights have been on my short list for a while. I’m now thinking of going with the TK75 even though it’s $70 more .
good choice :)
I was looking at getting a BS Terminator, but having seen the TK in action, this, and another review with the TN31mb, where the TK75 was the only semi-flooder to touch the target, went with the TK.
It's my most expensive light to date, and I couldn't be happier. One of the three LEDs is a bit off center, but I don't think it's affecting much of anything.