Review: Acebeam K40M MT-G2 NW 3x18650 Flashlight

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sb56637
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Review: Acebeam K40M MT-G2 NW 3x18650 Flashlight

Acebeam K40M

Reviewer's Overall Rating:  ★★★★

 

Summary:

Battery:  3x18650
Switch:  Forward clicky + mode control ring
Modes:  6 regular, 1 strobe
LED Type:  Cree MT-G2 neutral white 5000K
Lens:  Anti-reflective tempered glass
Tailstands:  Yes
Price:  ~$120.00
Link:  Acebeam.com
Date Ordered:  25-AUG-2014

Note: This light was provided for review by Acebeam

Pros:

  • Fantastically bright, single MT-G2 emitter
  • Excellent throw
  • Easy and practical mode control ring
  • Attractive design
  • No parasitic drain
  • Fairly compact for its performance category

Cons:

  • Fairly expensive
  • Poor labelling on mode selection ring
  • Attachment of the lanyard prevents tailstanding
  • Possible heat management issues

Introduction:

When Acebeam first contacted me about reviewing their new K40M, I frankly wasn’t all that excited. Lately I’ve been getting into high performance, neutral white tinted, triple XM-L2 flashlights. So when I saw that the Acebeam K40M uses a single Cree MT-G2 emitter, with no mention of the tint, I was expecting fairly marginal performance. But then again, it appeared that the K40M would at least throw well, and Acebeam is a premium brand, so I agreed to give it a shot. I’m happy to report that the performance of the K40M pleasantly surprised me by far exceeding my expectations.

The new Acebeam K40M arrived in a very nice padded case that measures about  24x14x10cm.



Inside, we find the K40M inside a sturdy case with belt loop, a standard clip-on lanyard, and a spare switch boot and O-rings.


The K40M is a bit bigger than I expected. It's definitely one of the heftier lights in my collection. Here’s a comparison to the other lights in my collection in approximately the same league:

 

Features / Value:  ★★☆☆☆

At around $120.00 shipped, the Acebeam K40M is fairly expensive on my absolute pricing scale. On the other hand, some lights with considerably less features cost quite a bit more.

The K40M comes with the standard accessories and a very nice case. The light itself features a Cree MT-G2 emitter with a very nice tint, both of which I consider to be premium features.  Additionally, the K40M sports a nice dual-orientation battery carrier, together with its most important feature: the mode selection ring coupled with a mechanical forward clicky in the tail. One of the modes is almost moonlight-low, which is very hard to find on these barn-burner high performance lights.

So all in all, I would say that the Acebeam K40M carries a fairly high price tag, combined with some very nice features. So let’s give it 2 out of 5 stars for its price to features ratio.

 

Design / Build Quality:  ★★★★

The Acebeam K40M arrived in almost impeccable condition. The aluminum-bordered case with its thick foam interior is a nice touch. The light itself came with flawless anodizing and uniform coloring, coupled with very nice knurling on the grip region. The threading on the battery tube is smooth and well lubed. The 3x18650 battery carrier looks and feels very sturdy.

     


A very important feature of the battery carrier is redundant positive/negative contacts, thus making it orientation-agnostic. This is a huge boon when fiddling around with a battery change in the dark, and it eliminates the danger of inserting the carrier backwards and damaging the cells and/or the light, to say nothing of the user.

The reflector of the K40M is deep and absolutely flawless on my unit, with no smut or other blemishes. The glass lens is also pristine.



An examination of the opposite end reveals a very minor flaw: The switch boot has a bit of rubber flashing, but it doesn’t impair functionality at all, and the spare boot is perfect.

 

The switch itself is a forward clicky, which works well in combination with the mode control ring. I really appreciate the fact that this is a mechanical switch where OFF is truly OFF, with none of the parasitic drain found on lights with an electronic “soft” switch. So the K40M is an excellent choice for those who tend to leave their lights in storage for long periods of time and don’t want to worry about it finding it trickle-uncharged when they need it most. The forward clicky also permits use of the light for signaling, if needed.

Speaking of the mode control ring, I think it’s one of the most appealing features of the K40M. It has six modes, ranging from a very useful moonlight mode (0.9 lumens according to the manual) all the way up to a scorching 3000 lumens. After the highest mode comes an OFF mode, which permits leaving the tail switch on but turning the light on and off using just the control ring. This seems like a very useful feature for one-handed or gloved operation of the flashlight. The last mode after the OFF position of the control ring is the strobe mode. This is basically a perfect setup: easy changing of the modes, plus an extremely disorienting strobe that can be easily accessed while still staying out of the user’s way when not needed. With my fairly large hands, I can maintain a firm grip on the light and move the mode ring with the same hand. The only quibble with the mode ring is the poor marking of modes. The ring has an arrow that lines up with an ascending ramp marking on the flashlight body, but it doesn’t point to the very bottom of the ramp on the lowest mode as expected. From there, mode #2 is near the top of the ramp marking, and #3 to #6 are completely off the chart. Subsequently, the OFF position of the ring points to a label that reads “Stand by Strobe” as though it were a single mode. Of course, the OFF position is meant to labeled as “Stand By” and “Strobe” is a separate mode. But I would prefer a timeline of sorts with finite dots that line up with the different modes. The ramp marking would seem to make more sense if it were infinitely variable, and even then it’s far too short and doesn’t correlate well with the actual light output of the modes.

As mentioned, the strobe mode is extremely bright and incredibly disorienting. One neutral observation about the strobe mode is that it has a stutter/pause every few seconds, which makes it seem even more random and disorienting.

I discovered that the K40M measures the battery voltage and warns the user by flashing the beam every 30 seconds or so when it gets low. Finally, it completely shuts off the light. My charger measured the cells at 3.14V when I put them in for a recharge.

I really appreciate the inclusion of a very low (practically moonlight) mode for the K40M. This is a feature that is often overlooked in powerful lights. After that, the subsequent modes are well spaced and offer a perfect selection of brightness for all situations.

 

I wasn't impressed with the design of the lanyard attachment. It's a standard latch-on style of lanyard, and the two lanyard holes on the tailcap are spaced too far apart to allow the lanyard to be attached tangentially. Instead, it must be clipped onto the perimeter of the tube, which interferes with the flashlight's ability to tailstand when the lanyard is attached.

Overall, the Acebeam K40M is very attractive, featuring a clean, functional design with no unecessary fluff. As mentioned, it’s fairly big. But its overall dimensions are proportional to the large head, which helps for heat dissipation and gives it room for a deep reflector that throws well.


So all in all, the Acebeam K40M is very well designed and executed, and makes for a very pleasant to use flashlight that exudes a feeling of quality. Well done, 4 out of 5 stars.

 

Thermal Management:  ★★★

Normally when I review flashlights, I give them a rating for battery life on the lowest mode. However, the Lithium-Ion battery chemistry, which can be damaged by overly low voltage, isn't ideal for slowly draining to 0 volts over a period of many days as I often do with my alkaline/NiMH compatible lights. Incidentally, the low mode of the Acebeam K40M is extremely low, and the user’s manual claims 1000 hours of runtime on that mode, which is superb. However, flashlights such as the Acebeam K40M are principally meant for using during a brief period of time, often on the highest mode. Therefore, we won't discuss battery runtime for the K40M. Rather, we'll discuss how long it can be safely run on the highest mode.

The owner’s manual for the Acebeam K40M claims that it has “intelligent temperature controlled light output for user safety”, which seems to indicate that it should kick down the brightness if it gets too hot. I’m still not too sure if this works in practice. I left it running on the highest mode, and after about 5 minutes the head was almost too hot to touch and no visible change in brightness. So I started to get nervous and shut it off. I imagine that on a cool night moving around outside, it wouldn’t heat up as much. But I’m not convinced that the heat managementment is good enough to protect this light from its own fierce performance. I would be interested in reading comments on this post: Do you think that the large amount of heat I felt is proof that the light is in reality doing a good job of shedding heat, or is it building up inside and potentially causing damage?

At any rate, 5 minutes of runtime on the highest mode is still useful in a lot of situations, and theoretically if I wasn’t such a chicken, the K40M is supposed to protect itself and me from thermal damage, so I’ll give it 3 out of 5 stars for this category.

 

Light Output:  ★★★★★

The Acebeam K40M is fantastically bright, no buts about it. It really surprised me when I fired it up for the first time, expecting something similar to a single XM-L thrower. Instead of that, it was immediately apparent that the K40M positions itself as one of the brightest lights in my collection. The user manual put the highest mode at 3,000 lumens, which sure sounds plausible, if not slightly conservative. I don’t have any equipment to test actual OTF lumens, but the most important thing is what appears to the eye of the user, and in the case of the K40M what appears is a whole lot of blinding light-- truly impressive for a single emitter light. Instead of posting lumens measurements and taking night beamshots, since I don’t have the setup for that, instead I’ll rate the brightness and throw of the K40M in comparison to other lights in my collection which you also might own. The closest contender is the BTU Shocker. Mine is the older generation XM-L1 neutral white edition. Light output is approximately equivalent, but the K40M gets the nod for slightly brighter output. Better yet, the K40M is incredibly well focused, and since it’s only a single emitter the center hotspot is clear, bright, and well defined. The triple XM-L lights, on the other hand, have a bit more trouble blending together the three beam profiles into a single hotspot. Such is the case during fairly close-range white wall hunting. Under actual real-word usage, the K40M and the BTU Shocker are very similar. In this context, the considerably more compact and agile K40M puts on a really great performance in comparison with the mighty BTU Shocker. They both throw extremely well, and they throw a lot of lumens. The owner’s manual for the K40M claims maximum beam distance of 509 meters, with peak beam intensity of 65,000cd. I have no reason to doubt this.

To me, even more important than the pure brightness of a light is its tint. I never stop marveling at the difference in accurate color rendering of a neutral white flashlight in comparison with the sickly, stark white light of a standard cool tint. The K40M doesn’t really advertise its tint anywhere, but it turns out that its tint is a beautiful creamy, neutral white color around 5000K. In my comparison photo of the big lights in my collection, the K40M, BTY Shocker, and Roche M170 are all neutral white, and I greatly prefer them over the Supfire M6 and the Sunwayman T60CS due to the tint. I’m not positive, but I believe that all or most Cree MT-G2 emitters have this same neutral white tint, which is a fantastic default in my opinion.

In view of all this, I can confidently state that the Acebeam K40M earns an easy 5 star rating in this category of light output. Very well done, Acebeam and Cree!

 

Summary:  ★★★★

In conclusion, the Acebeam K40M is fairly expensive, but not overly so. It offers some really compelling features, such as a bright and modern MT-G2 emitter with beautiful tint, modulated by an easy to use control ring and funnelled through a really throwy reflector. It definitely won me over due to its combination of manageable size and formidable performance, coupled with very high quality construction. An average of the four main review criteria comes out to 3.5, so I’ll happily round up a very nice 4 out of 5 star overall rating for a very capable and attractive flashlight. Thanks to Acebeam for the privilege of reviewing this!

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Edited by: sb56637 on 10/01/2014 - 13:27
sb56637
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M4D M4X
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nice review!
thanks Beer

 

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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.

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

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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. Smile

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.

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Thanks for sharing .

Nice review .

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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?

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how2
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Nice review sb but too expensive for me I would rather have the

Courui D01$29.99.


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sb56637 wrote:
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?

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 Smile .. 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.

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my9221
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Thanks for the lengthy reviews!

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how2 wrote:

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

Courui D01$29.99.


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

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Thanks RaceR! Great explanation.

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

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sb56637 wrote:
h3. More reviews (and much better than mine Silly ) of the K40M:

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!

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

some of my actual experiments and reviews:
UF-T20 review and mod —->http://budgetlightforum.com/node/30186#node-30186
My EBRZM, over 1 million cd thrower—-> http://budgetlightforum.com/node/30274#node-30274
Ervin’s try (2nd. Annual BLF Scratch Made L

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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.

 

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

 

djozz quotes, "it came with chinese lettering that is chinese to me".

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old4570 said "I'm not an expert , so don't suffer from any such technical restrictions".

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M4D M4X wrote:
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.

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.

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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

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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.

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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!

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