Review: Acebeam K40M MT-G2 NW 3x18650 Flashlight

nice review!
thanks :beer:

Gonna get hooked on the big MT-G2 like me! lol

Thanks for the look, makes it that much more difficult to resist. The K50 is proving out to be a very nice light in my collection, this K40M would be a nice sibling for it.

Thanks SB for the review.. it indeed is a very nice light.

Great review. Very enjoyable to read.

Yes, the light will become extremely hot in that type of indoor test due to the high emitter current.

It does have some output "sag" from the driver as well as a minor current drop that will limit heat a bit, but its still got very high output on highest setting. I have not seen any "thermal management" outside of that, if there is any, it must be at ridiculous temperature.

That heat is a "good" thing. The emitter is overdriven from the factory at the highest setting, so you want the light to become really hot instead of getting heat buildup below the emitter. The light have good thermal transfer (large DTP copper mcpcb, well attached to the aluminium head with screws and unihead design).

The Cree MT-G2 comes in several tints with different CRI and Chromaticity Region ranging from 2700K to 5000K. But it seems like close to all lights use one of the 5000K emitters. That is one of the good things about the MT-G2. There is no CW low CRI super output version. So even when the manufacturers go for the brightest coolest version available, we still get NW and decent CRI. :)

Btw, If your K40M is comparable to your BTU in the throw department then your BTU could benefit from an upgrade. IMO K40M is easily the nicer and better allround light. But long range high output lighting is something the BTU can excel at compared to the K40M.

Thanks for sharing .

Nice review .

Thanks for your insight RaceR! So do you think I can safely leave it on for longer than 5 minutes after it starts to feel hot?

Reminds me of chemistry class, I remember how confused we were when they taught us that a beaker that feels cold to the touch is actually an endothermic reaction, because it’s absorbing heat from hand, whereas a beaker that feels hot is an exothermic reaction because it’s releasing heat to the environment. So does a flashlight that feels hot necessarily mean that heat is actually NOT building up inside and thus is safer?

Nice review sb but too expensive for me I would rather have the

Courui D01$29.99.


External temperature is rarely a good indication to accurately say if thermal transfer is good. Put a 5A driver in the average P60 based flashlight and the light will still get stupid hot in no time, does not mean it have great or fantastic thermal transfer.

One way to tell if a light have good heat transfer is to measure light output and see how quick its declining over time. A well regulated light with good heat transfer will not drop that much. (Assuming its not a tiny extreme hot rodded light that gets stupid hot instantly). Naturally, as the light becomes hotter, the emitter will also become hotter, so there will always be some unavoidable heat sag that will happen over time. And to mention more of the obvious, the smaller the light, and the harder its driven, the more heat sag there will be, even if thermal transfer is good. Simply because everything will become hot.

What can be very misleading and something that many forget. Is that sometimes a light show lots of output drop, but that can be due to driver behavior from a supposedly regulated driver, or the lack of regulation. Basically you should know both the light output drop and the emitter amp drop in order to get a good picture. If you only measure light output drop on the K40M from startup it will look as if its got bad heat transfer/thermal capabilities, but that is not really the case since the driver is dropping output to the emitter.

Another way to get an indication of thermal transfer is to do a full teardown and look at the construction of the light. When that is said, peoples thoughts on what is adequate is highly debatable. An approach based on measured data is highly preferable.


Can you leave it on for more than 5 minutes at the highest setting? Yes, I would say so.

There are many reviews of this light on BLF. Just to take one. Skip to around 5 minutes 30 seconds in this video review, and you will see a full runtime test. As you can see. The light did not self destruct :) .. How uncomfortable it was to hold after 20+ minutes is another story.

In general I say if you hold the light without it being uncomfortable, keep going on highest setting for as long as you want. My main concern is typically the batteries, they should be kept below 60C. Under any normal real life hand held use there is no reason for concern since you will burn your hand before any good light should be anywhere close to damage. If you are using a "hot light" without holding it, don't use max setting for more than few minutes. Or just simply stick the lower modes.

Thanks for the lengthy reviews!

Courui is different grade in terms of emitter and brightness as well!

Thanks RaceR! Great explanation.

Nice review SB. if the price was a bit lower i would look at this one as a next big light.

hey, don’t put yours down. You brought home the appeal of the light WITHOUT drooling over some irrational intention of stripping the light down to its wires in hopes of replacing everything to satisfy some obsessively out-of-whack desire to get the light to perform in a way that voids the warranty and forgets real-world usefulness. You gave practical comparisons to show the appeal of the beam, its type and style, and the overall value of the product. I wish more of our reviews kept focus on these elements. We often let down our newer members based on fuzzy tech-spec talk and hobby geek-speak. There are a ton of great reviews and reviewers here, but I loved how your review touched on flashaholic factors, but did not neglect basic pragmatic concerns. Way to go!

Nice review, I have no intention to buy one but I have one similar light and pretty much agree on everything.

i have to comment rusty joes post…

if you don´t like reviews (or tear downs) that are different don´t read them …
i feel a little offended from your words.

i found so perfect done reviews here before i did mine - i didn´t want to do the same a 5th time.
all the good pictures and videos have been done by people who are more skilled than me (and use better equipment)

so i decided to risk my light to show whats inside for the modders and tweakers here in BLF

i do not want you to like that - but please dont about my work as i am an idiot.

Thanks sb. You have to love those big reflector MTG-2 lights.

Don’t be offended, friend. It’s just that entire threads can go by where no one really hits on the value of a light except to hobbyists, and I think we do the majority of our readers a disservice by being too hobbyist.

That doesn’t mean that modding and “playing” shouldn’t be done. I read those threads, too. But that - at the exclusion of more practical considerations - is not good. It just goes a little bit far sometimes.

Thanks for the great review. Really enjoyed reading that. I don’t think this light is expensive. If you compare it to other similar mt-g2 flashlights

Thanks for another of your detailed enthusiastic reviews. Its interesting that this light can compete with a 1st gen XML neutral equipped shocker at a fraction of its weight and size while providing a smoother beam. This one should be a great user.

Just got this light today and I love it! It truly is a retina-scorcher with boundless value, even at its original asking price.

Don't hold out, anyone!