Well, two variables: the LED and the MCPCB, but the IOS T6 is ~10% brighter than the U2. Both beam tints looked about the same, but I did not compare side by side yet.
So, is the FT U2 4C really that worse than a T6 4C? Hhmm, you'd have to look at other test data comparing copper (direct thermal path) to crappy aluminum. According to Match's tests (https://budgetlightforum.com/t/-/16621), it should account for ~6% difference I'm guessing at this amperage of 2.1A. Possibly in my simple test, maybe as high as 10% with variations, then you could only conclude the listed U2 4C is in fact a T6 4C, or maybe worse, a T5 4C? Match did use a 20mm SinkPAD, so could be characteristic differences in performance in this range of amps.
I was thinking this might have been done before... I had one of the FT ones in a bin, and was planning on using it in a zoomie upgrade (previous mod) and wanted to get an idea if any good. I like the neutrals soo much more in zoomies.
I have ordered some of those U2-4C, they are XM-L2 T6-4C, the T6 is the bin, the 4C is the tint…very neutral and the colors from the emitters are very vibrant and more “true” than with 1A…I have one in my Ultrafire SH98 on a 20mm sinkpad, and one in my Ultrafire F13 on copper sinkpad (both are epoxied to the pill) I just upgraded…at 3A~ they are INCREDIBLY bright and don’t have too much yellow in them or too much white…my favorite tint
My test results above in post #22 put it in the T6 or T5 range, just not sure. Didn't have time to move it to a Noctigon and re-test -- should have though... It's not a bad deal if it's a T6 at that price.
I think maybe they(cree) have some special U2/3 NW/WW (also very rare), but I don’t think it is commonly available. (needs alot of odd to get high bin in these warmy colour)
Oh by chance I put one of these in a crappy glove-box light with a 1.4a Nanjg 101 with a PMMA lens.
The tint is a very clean white overall with a very minute pinkness, almost can’t see it.
I’m not really experienced enough to comment on any other aspects of it though! I’m impressed at the brightness for 1.4a. Almost as bright as my H600FW being driven (factory) at 3.8a which kind of puzzles me.
I bought those XM-L2 “U2 4C” LEDs too, I don’t care much for the loss in brightness (since they are not real U2s) but FastTech (or any other seller) selling them as such is unacceptable.