I agree with cannga.
Pretty good overall assessment by cannga.
519A should be the most efficient and therefore offer the longest runtime (still pretty short, don’t expect long runtime from any of them). It’s the only one without the magenta-rosy tint that some enthusiasts love but many people (myself included) can’t stand.
I would disagree that the 519A (domed) and GT-FC40 are “rosy”. They are are both relatively neutral in tint, which for most LED use cases is desirable. The 519A is generally very close to the BBL in either direction. The GT-FC is fairly close to the BBL, but seems to have a larger range of DUV in samples. They will be “rosy” if you compare them to many other modern LED emitters that have positive DUV, but they don’t have an extreme magenta tint/negative DUV like the 219B. Obviously if you dedome a 519A it will be “rosy”.
I never said 519A is rosy, quite the opposite.
I could be reading it wrong, and in isolation, the 519A is probably more efficient than the B35AM, but according to L.R.O. reviews of the S21B 519A and the S21A B35AM the B35AM with the boost driver ends up being a more efficient system than the 519A with linear driver. I think.
ETA: Obviously, that’s not to say that there couldn’t be a more efficient 3V driver for a 519A. But from convoy, I like the B35AM.
In terms of efficiency at mid output, it is:
519A < B35AM <= GT FC40
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Comparing one with a Boost Driver and the other with a Linear Driver is a bit apples to grapefruit in terms of a comparison.
My B35AM in a Convoy M21B produces a lovely beam. However, I generally prefer the 519A beams. Whether one is more or less efficient than the other is really open to debate because both are close to each other when driven the same. I tend to think the 519A is more flexible in terms of power profiles and emitter output.
Good review with measurements [Review] Convoy S21A B35AM high CRI EDC flashlight . Outstanding CRI and R9 numbers, but 1100 lm is only low side vs GT-FC40. I have this light coming and will compare head to head with my GT-FC40 in same host M21B. I am excited about my B35AM light in MAO finish :+1: but if throw and brightness are what you’re interested in, from reading reviews I don’t believe it will match GT-FC40.
It seems CRI of XHP70.3 4000k per Simon is 70. And it’s a Cree (very high green hell potential). I would vote to pass or at least let other people be the guinea pig :innocent: on this one.
I carry and use flashlights, not loose LEDs, so the performance of the entire system matters. If the 519a is more efficient on paper, but commercially available flashlights with B35AMs get longer runtimes than flashlights with the same battery and a 519A, then that’s what counts to me.
Thanks for the replies. Not sure I’m really all that clear why you’d buy one over another still.
Not sure runtime efficiency really matters all that much. Not if using 18650 or 21700 cells.
Don’t suppose anyone has a side by side picture of the different LEDs showing their relative sizes?
Of course it won’t match the FC-40, B35AM uses 2x less power.
[quote=cannga]
There are some XHP70.3 with a CRI of 80 and 90 out there! 70 is the lowest I have seen and that tends to be on the very cool emitters.
I have a couple I'm working on from Simon, an L6 and M21F.
Which one of those would throw the most? 519a with dome one or B35AM?
Currently have a Convoy M21B GT-FC40 in 4500k which I love, but I would like something just a little more throwy, yet still high cri and warm tint. With the M21B MAO being available, I am thinking maybe getting another one of those, but would a B35AM be throwier than the GT-FC40?
In terms of throw in the same host, I will say throw will be 519A>B35AM>GT-FC40.
I don’t know, B35AM with it fairly compact domeless form factor and higher brightness may thow at least equally good.
Maybe just get the M21A or E?
Does anyone have an opinion on what the best GT FC40 host is? Seems like it needs a certain amount of thermal mass and battery capacity to truly “shine.”
Currently I have an 1800-2000k FC40 in a Convoy L6. It’s great, but the size to performance ratio is lacking for a spoiled person like me. Maybe the size to performance ratio would be just fine with the cooler temperatures. Still, I’m not convinced that L6 is the best host in general since its heat-sink fins are so shallow in the driver area.
I have B35AM in a couple weeks and will compare throw against GT-FC40 in same host, M21B.
Another choice as mentioned by phantom23 is M21E. It is noticeably more throwy than M21B. I don’t have the numbers with me but roughly IIRC it’s about 280m for M21B and 330m M21E. (Please don’t quote me on this; I measured all 3 but somehow completely forgot to post in my other thread.)
I too much prefer “smallish” lights. I have M21B, F, and E all with GT-FC40 4500k. E is noticeably most throwy, and the larger head is not too cumbersome. I use it most often because I like to see further ahead in my evening walk. And I tend to like throwy light.
B has dimmest hotspot but brightest spill (most floody)
E has brightest hotspot and dimmest spill (most throwy).
F is in between, but leans more towards B.
This LED doesn’t seem to burn up everything in sight like SBT90.2 :person_facepalming: 
. Thermal mass always helps but IMHO not that critical, at least among these 3 lights. Sustained brightness from Turbo run is around 37% of max, the smaller M21B just steps down a bit sooner. None of the 3 lights becomes excessively hot as with smaller lights. Hope this helps.