Observation from “real life” (not white wall hunting) use:
The M21B w/ B35AM is the coolest running Convoy flashlight I have, by a wide margin, clocking in at 42° C after 30 minutes continuous on from a Turbo start at home. In actual use (Turbo start then leave light alone during my walk), the S21D w/ Nichia 219b becomes almost/kinda too hot to hold in current LA weather, M21F is second, a little cooler but still quite hot, but M21B is acting as if it’s just loafing around.
Even more surprising, it is THE coolest running flashlight I have including other brands. At 42° C it acts as if it’s running at half throttle. I almost wish for a higher voltage (edit: current, thanks phantom23) than 2.4 A but I understand bad things did happen at higher current so unfortunately that won’t happen.
Allow me to post another picture of this very pretty light, together with my other latest Convoy light, M21E with Getian GT-FC40 at higher CCT 5500k. It is EXACTLY the light I have been looking for, a Nichia with throw and I recommend extremely highly (I love it).
B35AM may appear to run cool but partially that’s because of poor thermap transfer (that’s why Simon had to reduce current from 3A to 2,4A - emitters were frying).
Questions please: Why would it have poorer thermal transfer than say GT-FC40 in same M21B host (ie same design)? My GT-FC40 in M21B stays at 60° C.
Also this is a 30 minute run so the thermal transfer can’t be that poor, can it? Wouldn’t it fry the electronics if all that heat does not escape after 30 min?
Poor heat transfer between the emitter and PCB. There are no dedicated PCBs for B35AM, flashlight manufacturers need to improvise but thtere’s no good solution as of yet. So yeah, the emitter itself is hot it just transfers less heat to the body. That’s one thing. At 2,4A it uses 50% less energy than GT-FC40 so it has to run cooler.
@cannga: what is the ambient room temperature when you did the tests? The equilibrium temperature of a running flashlight depends heavily on both amount of power dissipated by the light AND the ambient temperature--leaving out the latter makes it impossible for us to deduce how much an identical light would heat up in our usage, as our ambient temp might differ much from yours.
It’s good you’re taking an interest in this. Nothing unusual 70-75 F. But let me rerun the test with all 4 lights (M21B with B35AM and FC40, M21E and M21F with FC40) in same condition tonight just to make sure I haven’t screwed up somewhere.
Are you thinking convection heat transfer also as a method to check what the temp inside is? Would shooting at the lens provide a clue also for internal temp? I will also take the lens off and check the LED, but it might too hot (upper limit of my IR gun is 60 C).
From Simon 4/17/2022
I’m sorry about the smoke from the B35AM. I have tried to find MCPCB with high thermal conductivity, but without success, the thermal conductivity of the MCPCB insulation layer currently used is 1.0.
I adjusted the output current of the driver to 2.4A and the LED no longer smoked.
I will be producing a batch of 22mm B35AM custom drivers with an output current of 2.3A.
Interestingly enough, the smoking was observed AFAIK in S21a (anyone pls correct me as needed), a smaller light than M21B. That combination of S21a and B35AM was released around 1/2022. After the above post in 4/2022, the current was reduced to 2.4A.
My M21B version was released AFTER the reduction, so it never went through the “Armageddon challenge.” You think it might just tolerate the higher current since it has a larger thermal mass? From actual use, seems like this M21B is just loafing during a Turbo run-down, with excellent sustained brightness.
Thank you for the reference! I am very interested in seeing how the re-run turns out. My room temp is probably hotter than yours, and my S2+ 519A triple running only 700mA mode gets noticeably hotter than body temp after half an hour. On the other hand, it's below 45F outside, and my C8 running SFT40 on ramping driver can sustain turbo indefinitely.
I have no idea if convection heat transfer works. I don't have any knowledge or experience using an IR gun. But my guess would be to avoid reflective surfaces like the lens. I would be very curious to see your LED temp measurements!
Convoy lights were re-tested @ room temp 26 C. I tail-stand the lights and start at Turbo level, then measure temp in next 30 minutes by pointing IR gun at the flashlights’ head, about 1 cm away.
The S21D with 519a immediately heated up to 60 C (limit of my IR gun), within ~5 minutes. The other lights (M21B x 2, M21F, and M21E) reached equilibrium at around 20-25 minutes. Temps at the end, 30 min after Turbo start:
M21B w/ B35AM: 42 C
M21E w/ FC40: 44 C
M21F w/ FC40: 50 C
M21B w/ FC40: 57 C
Glad I did the test; didn’t realize that there is such a large temp difference between the larger M21E versus M21B. I have all 3 so it doesn’t matter but if I have to pick one out of these 3, for me this is another reason to pick M21E over the other 2 FC40 lights.
Holding the flashlights with cooler temp is obviously more comfortable. S21D with 519a too hot to handle inside house, and better outdoor.
I tried to measure at the lens and also the LED directly after taking lens off, but it was too hot, beyond limit of the IR gun (60 C).
@Caleb thanks for the kind words. I’ve learned A LOT from people on BLF also - MANY souls here with “scary” deep LED and flashlight knowledge.
It is so interesting that the Convoy lights, once they hit auto regulation limit of 55° C, seem (ie speculation) to go down to a certain brightness level (~37% of max the few times I’ve measured w/ ceiling bounce) and stay there, almost seemingly regardless of the resulting temperature. For example S21D settles at 60 C, whereas M21E goes to 44, both with brightness ~37% of Turbo start.
What I find interesting is that although Tmax is 55 C, S21D steps down but then stays at 60 C externally. (Not complaining at all. I am a HUGE Convoy fan for this reason - it brings uniformly high sustained brightness.)
Next I would like to do the same temp measurement as above except starting not at Turbo (100), but at the next lower power level, 35 for rear switch, and 40% for e-switch Convoys.
I know it doesn’t make sense but sometimes I feel like (ie not sure) +starting at the lower level 35+ results in a cooler light than starting at Turbo and then let it stepdown to 37. Even after 20 minutes for equilibrium. Not sure about this though, it’s just subjective tactile eval so probably the test will prove me wrong.
Thanks MHCL (btw I remember your forum name from the very beginning of joining BLF ). On the topic of B35AM vs GT-FC40 in M21B host, I would like to add some observations from actual use:
1. In short duration use, say on for just a few minutes then off, the M21B w/ GT-FC40 is a noticeably brighter light than M21B w/ B35AM. FC40 has wider hotspot with about equal intensity, and much brighter spill. So no, IMHO B35AM has not replaced GT-FC40 as the ultimate all round walk-light LED.
2. For the way I use my flashlights (Turbo on at start of my walk then leave light alone for next 50 minutes - basically a Turbo run down), after about 10 minutes the M21B with B35AM catches and passes GT-FC40, by a little bit. I know Convoy runtime curves typically indicate flat lines, but in actual use with subjective observation, B35AM passes FC40 once step-downs kick in, by a little bit. IOW, IMHO there is real penalty in that heat generated by FC40 in M21B (partly why I prefer the larger M21E w/ FC40, which I’d recommend without reservation).
3. Where B35AM might be considered “better,” is that one, if you are just collecting Nichia’s, then it’s the rare “Nichia with throw” in M21B host (the 260 m throw is seriously good in use), two, sustained brightness in ACTUAL use is fantastic (among the very top), and three, it is more rosy than GT-FC40 in white wall hunting. In real life use, they look awfully similar tint wise, and both awfully close to 219b, to the point that I feel I may not pass a blind test. It is not like comparing 219b 4500k to some Cree LED w/ awful green tint at all. At this level these are all fantastic LED’s and I don’t think one could go wrong with any of them. Or ALL of them (grin).
Hi cannga,
I noticed the same, FC40 generates a lot of heat on turbo and next time I want to try to replace the thermal paste with the MX4. I have already done this operation on the IF25A and I noticed a fair runtime improvement.
Back in March 2022 when I was deciding between the available FC40 lights, I asked Simon about the difference between the small M21F vs larger M21D. His answer rings even truer now after these temp checks; from Simon (underlining is mine):
>>>>>>>>>>>>>
Compared with the M21F, the light output of the M21D is more concentrated.
The main thing is that the M21D has a stronger cooling capacity.
>>>>>>>>>>>>>
I think this is an excellent post by @phantom23 that might have been lost among all the pics I’ve posted on this page. Great data; phantom23 sure did his homework. :+1:
Underlining is mine for people trying to decide between the 3 available LEDs in M21B host: B35AM, GT-FC40, and 519a. These are emitter lumens so supposedly I should subtract 15-20% for optic/optical loss??
For me, output of 519a, 1250lm minus optical loss, makes me a little hesitant to get it now, even if available in M21F. If I am not reading the data right anyone pls correct as needed.
Beamshots of the 3 LEDs, a few seconds after Turbo start and some IMHO’s after more usage:
S21D w/ 519a 4500k (measured 3900k): Floody beam and perfect for close up work. 519a in actual use looks like a very nice warm golden color to my eyes, not quite peachy as seen in beamshot. My 519a 4500k’s CCT measures a lot lower than spec and that affects the color obviously. Maybe my next 519a I will order 5000k so it will hit 4500k?
M21B w/ B35AM 4500k: Very throwy, with an intense smaller hotspot. There are 2 LEDs I have that look most like 219b 4500k (the rosy tint), first is E21e, second is this one. This is the “219b with throw” LED if that’s what you’re looking for. The magenta/rosy tint is quite obvious in the spill, just not as strong as 219b. I love the throw AND the sustained brightness. The beautiful rosy tint and remarkable (highest I’ve seen in a LED) Ra=98 and R9=99 values make this a very, very compelling light to own.
M21B w/ GT-FC40 4500k: Very much the brightest of the bunch. Hotspot wider AND spill brighter (larger and brighter area of illumination) than B35AM. Hard to believe that after this initial brightness it will subsequently thermal step-down to same level as B35AM, at least in M21B host. The beam color in actual use also resembles 219b, but leaning towards the neutral tint of 519a. The brightness and throw of GT-FC40 still make it the go-to walk light for me, ie not yet dethroned by B35AM.
great info about the LEDs tints, outputs, and beam styles
thanks for the photos and descriptions,
a few well chosen words, easy to understand…
the pics really help too
the gtfc40 looks like a great walking beam… the wide floody profile is probably more relaxing to use, requires less aiming and re-aiming, than a smaller hotspot swinging back and forth across the trail.
I much prefer lights with USB-C charging and side switch so next light will likely be the new Convoy replacement for S21D. Prob 519a 5000k and 219b 4500k. For these 2 LEDs, I like the brightness and floody beam of the quad LED arrangement in S21D host.
I only bought (rear switch no USB-C) M21B w/ B35AM because of the extremely intriguing LED and I was too impatient to wait. Would have preferred B35AM in M21F host, a perfect combination to me, but Simon so far has no plan for that.
Sorry I don’t have much experience or opinion with sub 3500k CCT lights. I have Nichia 219b 2700k and 3500k in Emisar D4V2, but no other similar LED to compare them too, and for me comparison is the most fun & “important” part of the hobby.
