Review: Acebeam K40M MT-G2 Q0

Acebeam K40M MT-G2 Q0
graciously provided by for review

Many pictures include links to a larger size or have mouse-overs for more details or comparisons

MFG specifications:

Brand/Model Acebeam K40M


3000 Lumens

Beam Intensity

65000 cd

Working voltage

Batteryconfig 3x18650
Switch Tail-cap
Modes 6
Blinkies Strobe
Mode changing Mag.Control
Anodizing HAIII


Lock-out No
Momentary On Yes
Lens Coated
Reflector Smooth
Waterproof IPX8
(provided for review) Thank you!!

What you get:

The K40M comes in a nice hard carrying case.. of better quality than the UltrafireM51.
It included the K40M, holster etc.. and has even some cutouts to include 3 (spare)18650 batteries...
The padding is pretty stiff and hard, almost plastic feeling, which will protect the light and I believe the case as well. The included holster, spare O-rings and papers finish it off.

The holster is great, and fits the K40M perfectly. Unfortunately due to the weight of the head, the light will tilt when attaching it to your belt facing it up. You could choose to carry it head down, but you`ll need to be careful opening the holster, because it could fall out.

At first inspection I thought it included a Lanyard, but its more of a neck cord.
It can be attached with a clip, but if you want, you can attach any kind of (para)cord, as it has 2 holes next to each other.
It attaches with a claw clip, which will damage the anodizing already after a few uses.. or even by just attaching the clip to the tail cap


The body of the K40M is about the same diameter as a regular “soupcan” light, like the SRK, supfire M6 etc.

It`s therefore not very easy to hold for people with smaller hands.
Using the tailcap switch (which I usually really like on lights with electronic side switches/control rings) included using the magnetic control ring, you really need to use 2 hands to operate it.
Which could be a Con for some.
The Ultrafire M51 on the contrary is controllable by just 1 hand.

In one of my next posts, I will compare the 2, K40M and M51 and the choice (apart from price) would not as easy as it seems. With the M51 having to offer a few characteristics, that the K40M is missing.

The balance of the K40M is a little heavy headed, so it feels a bit unbalanced compared to other lights.


The manual states: Tactical knurling for firm grip.
My hand says: so so knurling for so so grip.. or in other words.. not so much knurling for not too much grip.

No, the K40M doesnt feel smooth.. and no it won`t slip easily out of your hands. But for this size light, and for the way of using this, I would choose a heavier knurling, and especially thinking using this is the Law enforcement and search and rescue, it would probably mean, the light would possibly be used wearing handgloves.
In which case they need more grip!

But the knurling that is done, is done very well.. No mismatch/no missing parts.

Anodizing, threads and prints

The anodizing is done properly across the light. Every spot and corner is anodized ,just like you would expect from this high quality flashlight.
I couldn`t find any blemish, nor any missing anodizing.
It`s a great looking light, and during my holidays, everyone who saw it at my parent`s house, just had to touch it!!!

My first impression was very positive, except for the prints.. The Acebeam letters are printed pretty badly.

The difference in colors above is not a difference in anodizing, just the lighting.
But after posting this picture in the K40M community thread, people told this was done on purpose.

Because It`s the exact same as their Acebeam LOGO.. which can be seen here:

Although its a 1 on 1 copy, the logo on the flashlight itself doesn`t look so nice..

I assume most people would think the prints are done badly....Just as I thought..
especially if they haven`t seen Acebeam`s official logo
Maybe this wasn`t Acebeam`s best choice!
The Letters on the other side are nice crisp and clear!

Another thing that could be improved would be the brightness indicator from Low to Max.

as it doesn`t cover all the output levels. There is a indicator, but only for the lower levels 1-3.

Then there is a empty spot,4-6 until it reaches the Standby and then Strobe.

The words Standby and Strobe are so close together, that someone who doesn`t read English could think its 1 sentence.
A few dots would have helped, or even symbols!! See pictures above.. click for larger size.

Threads are good... period

Buttons/Magnetic control ring

The K40M has a Power Switch at the tail in the form of a forward clicky. Which indicated it can be used as a Momentary On.
The Magnetic control ring has indents for every level of brightness, starting from the lowest to highest. Until it reaches the Standby indicator, followed by Strobe.

When you hold the light with 1 hand, you probably would be able to change the output, but it doesnt work so smooth. At the same time it`s very very hard to activate the tail cap switch with 1 hand. You better use 2 hands to Power the light as well as changing its brightness.

Changing the brightness using the control ring feels very solid. A big plus for Acebeam who has done very this well. Operating the ring feels very smooth, and each indent has a very clear difference in output.

Lens, bezel and reflector

In the following picture you can see that it has a smooth reflector, for improved throw.

although the reflector is smooth, it isn`t super duper smooth. Look at the mouse over for a better close up.
You can see rings,or some kind of artifacts. Probably due to it being made of aluminum.
Funny to say, but I have seen more pure smooth plastic reflectors than aluminum.

  • Diameter outside 70mm
  • Diameter inside 63mm
  • Depth 52mm

The lens is coated, about 3.6mm thick, and is described as ; Ultra clear tempered glass lens with anti-reflective coating.

The manual doesn`t tell anything about the bezel, but its clearly not made of Stainless steel.
During my photoshoot, and water test, I bumped it into some rocks, which left some blemish in its anodizing, and in its aluminum of the bezel. So it`s not as tough as a stainless steel bezel.

The bezel (as well as all other outer main parts) can be unscrewed, and has NO GLUE.
(note that the driver IS GLUED, and can`t be taken out easily)

Battery carrier and tailcap switch:

Its has a battery carrier with 3 batteries in series!
Which can accommodate unprotected as well as protected cells.
Unprotected cells are not recommended with batteries run in Series.
Plus they sit kind of loosely in the carrier.
Protected NCRB are very tight fit... Maybe its because I had made a short using trying to measure tail cap current, and got the springs damaged... and discolored..
Fortunately I had Unprotected cells, so they quickly stopped making contact... and saved me a light ;)

And due to the little buttons on the driver, the driver can be used with FLAT TOP cells.

The Postive contact touches a beefy coiled spring on the driver side.
The Tailcap can be unscrewed and has NO GLUE..
see pictures of the tailcap. This picture , another one and HERE, plus this one

Dimensions and weight:

Length 185mm
Diameter head 76mm
Diameter body 49mm
Weight empty 497 grams
Weight loaded 642 grams

The K40M consists of 2 main pieces..
The Head and the body.

The head weighs 320 grams
The body + batteries weighs 322 grams

UI and modes

The K40M has 6 main modes, a Standby and a Strobe mode.
Starting from the left of the control ring, you`ll have
Levels 1-6, a Standby mode, and at last a Strobe mode.
Nothing hidden. Very very easy to understand and operate!! Again a big Plus for the K40M.
Anybody can use it!!
When left in the Standby mode, you have instant access to:

  1. Turbo (dial left)
  2. Strobe (dial right)
  3. Low, if you dial it counter clockwise quickly which wouldn`t show any light in higher modes.. unless you`re turning the ring slowly


  • Strobe


NONE!!! that I could detect

Lock out

No, and it doesn`t need one.. Because it has a clicky switch on the bottom for complete off.
As well as a Standby mode, for instant access to High and Strobe.


Measured with 3x NCR18650B panasonic 3400mAh protected.

Ceiling bounce in lux

Level 1

Level 2

Level 3

Level 4

Level 5

Level 6















Lumens mine







Lumens Manual







Lux ceiling bounce
Level 1: 0 lux
Level 2: 3 lux
Level 3: 60 lux
Level 4: 154 lux
Level 5: 263 lux
Level 6: 426 lux

which equals in %
Level 1: 0%
Level 2: 0.7%
Level 3: 14%
Level 4: 36%
Level 5: 61%
Level 6: 100%

Lumens in table, if 100% is 3000 lumens
Level 1 is in my understanding and comparisements NOT 0.9 lumens, but a Few lumens

Current Draw

I got a spark and the springs on the battery carrier overheated, which resulted in no contact with my unprotected batteries, while trying to get a reading at the tailcap.
Now the springs are shorter,so I will only use protected batteries.

I think that I was lucky not using protected batteries, as something more serious could have happened.
So, if you get one of these, DON`T try to measure current on the pos and neg of the battery carrier at the tailcap.
Just read that you should be able to measure it with the the probes touching the threads/body of the light instead of the battery carrier.

So I have no numbers!!sorry


I had done 3 full runtime tests.. 1 in Level 6...
1 in Level 5 which failed because I forgot to set up the electronic remote control switch of my camera on timer.. and the 3rd one, Level 4, I had set up the remote control for TOO few interval stopped taking pictures before it ran dead.

At the time of writing I`m doing another Level 5 runtime test.
Tested with a set of Panasonic 3400mAh protected cells.
I took pictures of the output in Lux (ceiling bounce) in 5 minute intervals.
See the pictures below

Level 6: max:

Click above for LARGE size

A runtime of 65 minutes..
Using 2 small laptop cooling fans
The output drops quite a bit within the first few minutes..

Just before the 1 hour mark, the K40M starts to blink as a Low Voltage warning.
And at 1 hour and 5 minutes the light turned off automatically. (65 minutes)
All batteries were just below 3V.

The BT3100 charger didnt want to charge them... but when you select Discharge Refresh it started to charge.

Next: Special close up of the first 9 minutes without cooling

Interval pictures at 10 seconds
click on picture for Large size
This time still used the unprotected Sanyo 2600 cells.

And all the info in an easy graph:

The output has a drop of about 20% in 10 minutes time.. Compare with output difference before with Pana 3400 cells. The 9 minute test was done WITHOUT cooling.

Level 5:

Click for larger pictures

Another graph to understand the runtime a little bit better:

Runtime is 115 minutes, which equals to 1 hour and 55 minutes

THROW: Measured at 5 meters in Level 6

    • 62500cd within 5 seconds
    • 57250cd after 30+ seconds

Beam shots:

Taken with a Fujifilm F200EXR on Manual setting ISO400 f3 ½ second

Click on pictures for little larger size

Control shot:

Level 1:

Level 2:

Level 3:

Level 4:

Level 5:

Level 6:

More shots, now taken on Manual setting ISO400 f3 1/5 second (to lessen the overexposure)

Control shot:

Level 1:

Level 2:

Level 3:

Level 4:

Level 5:

Level 6:



  • Great value for the money at banggood
  • 6 output modes
  • Magentic control ring with indents to adjust brightness
  • The Low is low enough (for me) on this type of light
  • Not glued
  • Tailcap switch for permanent Off
  • Standby mode, so a 1 handed operation is doable (not that great)
  • Low voltage warning
  • Throws fairly well stock!
  • Carrier can hold Flat and Button top cells...


  • 20% output drop within 10 minutes (although impossible to see by eye, because it goes slowly)
  • Grip (the knurling is very well done, but not very aggressive, could be slippery in some circumstances)
  • 2 handed operation is almost inevitable.. Very difficult to control the light with only 1 hand
  • No stainless steel bezel
  • Smooth reflector is not completely smooth, but has some sort of rings (spots)
  • Weight is a little balanced towards the front, but if you have nothing to compare it with, it isn`t so obvious
  • Indicators for brightness levels are missing, and Standby and Strobe are too closely printed

Small photo gallery:

It did survive the 1 minute water test ;)

Useful links:

  1. Acebeam website
  2. BLF: Inner parts revealed, and modded by M4D M4X
  3. BLF: Video review by mhanlen

A comparison between the Ultrafire M51, and the Acebeam K40M review

Comparison, size and output

first some day shots... to show the difference between the Ultrafire M51 and Acebeam K40M

The head of the K40M is much larger. And because of the Smooth reflector throws quite a bit farther than the M51.

The Ultrafire M51 measured 31175cd
While the K40M measured about double the M51 at +/-60000cd

The K40M has double the throw, and about 1000 lumens more output.

The M51 will give you 95 minutes of runtime in Max.
The K40M will give you 65 minutes of runtime in Max.

Throw comparison/Beamshots comparison:

Mouse OUT K40M,,, mouse OVER M51

and throw

The M51 is a little "warmer" than the K40M..

Acebeam K40M Ultrafire M51
Modes 6+strobe 4+ strobe
UI Simple with mag control Not very good
Stainless steel bezel No Yes
Holster Yes, (soft) Yes, (hard)
1 handed operation Not really Yes
weight 642grams 642grams
Balance Front heavy Well balanced
Size X O
Throw 62500 31750
Output +/- 3000 +/- 2000
Runtime max output 65minutes 97minutes
only in max modes on both lights
Grip X O

If you just want a great light with an MT-G2, and don`t care about stainless bezel, more pocketable etc... go for the K40M.
But the M51 has some advantages as well...
Very easy to operate with 1 hand, and more pocketable.
Runtime in MAX output is longer, but has less output.
But you would always be able to get at least 1.5 hours of runtime on the M51.
Although the weight is the same, its balances better on the M51, as well as the knurling.

So they are different lights..
I still think the K40M will give you more value for the money.. but the M51 has some characteristics that could be Better for Some people... so don`t rule out the M51... especially if you can find one for a good price below the $100 mark.

Great review ChibiM.
What’s the difference between the MT-G2 QO and the MT-G2 PO?

It seems like its just a higher bin, the higher the letter, the higher the bin!?



this document by Cree doesn`t show the Q0 bin (yet)

Nice review and good pictures. As always! ;)

Appreciate the bonus comparison as well. :)

Just some questions/nitpicking.

You say there is no glue on any of the main parts and that they can be unscrewed. Wasn't the driver compartment screws sealed (and probably used loctite on)? They were on my light.

You say runtime on Ultrafire M51 is an advantage. But, you could just set the K40M on level 5 and have roughly the same output and runtime? I dont know how the lowest mode is or efficiency on low on the M51 is (did your review cover that?). My guess is that K40M does have the advantage when it comes to max runtime (on lowest level). If that is the case, im not sure how the M51 have any real advantages in terms of runtime.

Thanks for the review ChibiM! Very valuable information. A few questions and comments:

  • Other people might disagree, but those small pictures showing the diminishing output aren’t useful to me. The differences are too small for me to see. The graphs are great though.
  • In the sentences I’ve quoted from your original post above, there seems to be some contradiction. Could you clarify what you mean please?
  • About the brightness indicator, my guess is that the “ramp” image isn’t supposed to cover modes 1-6. I think they just used a small ramp image that you could see at a glance. Similar to an On/Off switch that’s labelled “0/I” at one end, but isn’t labelled at the other end.

Excellent review! Very thorough!
But for one thing, at the very beginning, it says working voltage ~4V. Isn’t the MT-G2 a 6V emitter? But of course we know that it is. Looks like a factory mistake. :wink:
Nice pics, very detailed work.

Nice reviews with beautiful shots. Ebay sellers may accept your offers with better price!

Perfect review with lots of pictures and useful data.

I agree they all look the same. Maybe putting them in a animated gif will be more relevant ?

Infact it has less runtime than K40M with level 5 which is similar to M51 max.
The Acebeam use DTP copper star ?

Great photos, ChibiM. And nice review to boot :slight_smile:

Thanks for the detailed review mate

VERY detailed and fluidly relevant review. Also, nice formatting!

So an actual 3,000 lumens?! Wow.

Thanks for reading the review!

Good you ask me those questions..

Yep, you are right about the driver.... But I was more referring to the "main parts, as body, bezel, and tailcap.
The driver belongs in the "special inner parts" ;)
I will edit the text, and make that clear, that the inner parts are glued!
Tried even to get the glue out, and remove the driver.. but without success.

Again you are right..
at this point, I was referring in the comparison the runtime in MAX mode.. regardless output..
Kind of like this: The Minimum runtime on the M51 is .......minutes.. vs .....minutes on the K40M.

Again, will make that point more clear in the review!

K40M will have longer runtime in Level 4, than M51 in Max.

Thanks for the questions as well.
Could you please explain where the contradictions are?

I`ll try to explain (not 1 by 1) what I mean, maybe that would clear it up.

The UI is very easy to understand! and can be used by anybody! (as long as someone has a working memory ;) )
It is very easy to change outputs, and therefore its a big plus!!!
Compare it to lets say; Eagletac lights, or lights with hidden modes.. people could have trouble just remembering how to change modes.... same like with the M51, which UI isn`t really the best.

The light can be operated by only 1 hand, but I assume that this light is designed for that.
So I mentioned that it is really hard to operate with only 1 hand, and in comparison to the M51 that could be a CON.
But at the same time very reliable and easy to operate with 2 hands.

So when I refer to the good sides, I imply the use of 2 hands...

the rest (negative) is referring to a 1-hand operation.

Yes, I didn`t know how to "name that little brightness indicator".

about the pictures:
Just showing the steps of output difference can still be seen in the smaller pics.. and in the second post I have comparison pictures with the M51, which are bigger.. on purpose, as I think its more relevant then.

I just didnt think I wanted to take so much space in the review with just beamshots of the 6 levels. I hoped the output difference would be understood with looking at the table.

Yes, I just copied that from the Manual.

I personally think it can`t work lower than 9V.

will change that in the list of specifications

yes, the runtime has been mentioned by Racer86 as well, and I explained it in my reply.. its the longer runtime in its max mode.. (although with lower output)
Yes, I measured it and its DTP..
I put 1 probe besides the MT-G2 where it has a little blank space of copper, and the other one on one of the screws, and it had continuity....

Thank you ChibiM, I understand now.

Thanks for the hard work, well done.

Great review!! Seems like a solid performer.

The one thing I don’t like is that for about the same diameter they could have used 4 cells in 2S2P instead of 3.

That`s 1 thing I also thought.. its the same diameter as a SRK.

Maybe they wanted to have more headroom for more Vin... not sure what the reason would be.