Review: AceBeam K40M MT-G2/3*18650 Flashlight

AceBeam K40M MT-G2/3*18650 Flashlight

* K40M provided for review courtesy of

The Acebeam K40M is an upgrade to the K40 XM-L2 model and is Acebeam's answer to the ThruNite TN35.



  • LED: Cree MT-G2 LED with a lifespan of 10+ years of run time
  • Max 3000lumens output (3x 18650 batteries)
  • Output (select by magnetic ring):

Level 1 : 0.9lm(1000hrs);

Level 2 : 42lm(70hrs);

Level 3 : 430lm(11hrs);

Level 4 : 1150lm(4.5hrs);

Level 5 : 1900lm(1.5hrs)

Level 6 : 3000lm(0.9hrs);

Standby : 65uA

Strobe : 3000lm;

  • Working voltage: 4V - 13V;
  • Max Runtime: 1000 hours;
  • Max beam distance: 509meters;
  • Peak beam intensity: 65000cd;
  • Impact resistant: 1.2meters;
  • Waterproof : IPX-8 Standard;
  • Size: 186mm(length) x 76.2mm(head diameter)*49mm(tube diameter);
  • Weight: 451.5g(without batteries);
  • Aircraft grade aluminum body structure;
  • Premium type III hard anodized anti-reflective coating;
  • Accessories include:
    • 1x Replacement O - ring and Tailcapgummi; 1x user manual; 1x holster; 1x lanyard; 1x warranty card

Product Description:

  • Integrated cool fins design provide better cooling;
  • Smooth polished reflector creates maximum throw;
  • Aircraft grade aluminum, mil-spec hard anodized for maximum wear;
  • Large cooper heat sink pad for superior thermal conductivity;
  • Magnetic ring control switch allows you to select desired output easily;
  • Mechanical reversed polarity protection design for battery carrier;
  • Intelligent highly efficient circuit board design for max performance and long run time;
  • Ultra-clear tempered glass lens with anti-reflective coating, which achieves a 98.3% light transmittance.



Build quality is extremely good. The UI is one of my very favorites: a magnetic control ring to control output and a forward-clicky tail switch for momentary on and as a master power switch to negate any parasitic drain from the electronic driver components. The control ring is not one with infinitely variable output control. It has defined output levels with 6 brightness levels, Standby, and Strobe. It fits well in hand and is nicely balanced.

The best way to discuss the light is to look at the pictures and add comments. Right about now is a good place to start...

^ The K40M arrived in a nice case. Nothing was bent or damaged on the exterior and the lid fit properly and the latch closed properly. The handle is the same used in many other cases I've had lights come in.

^ Inside the case is a padded lid and a dense, custom cut foam insert in the base. The K40M was installed in it's holster which in turn fits very snugly inside the case. A smaller compartment cut into the foam holds a small Ziploc baggie containing a spare silicon switch boot and two spare O-rings.

^ The holster fits the light well but the top flap is a bit too large for it. It appears to be the same holster used for other large models like the K50 but the Velcro still just grabs with the top flap pulled snug.

^ The belt loop is designed with a closed loop plus a Velcro and snap closed loop to be mounted without removing your belt or to accommodate larger web and utility belts.

^ The bezel is aluminum and has small, smooth edged crenelations so you can see if the light is on if placed head down.

^ It's a great looking light with hard mil spec black anodizing with a matte finish that I prefer over shinier anodizing. The K40M is a handsome light with great feel and proportions.

^ The laser etching is some of the best I've seen.

^ No, the etching on the logo isn't damaged or defective. It matches the Acebeam logo used on their website.

^ The knurling on the K40M is fantastic. It's aggressive and grippy without being too rough. All machining is perfect with no machining marks anywhere on the light.

^ The magnetic control ring is fairly stiff but engages each mode with a defined "snick". Visible above are the markings for "Stand by" mode and "Strobe". From "Stand by" a click to the left goes straight into "High" or a click to the right goes directly to "Strobe" mode.

The only marking on the control ring is the arrow seen above. With the ring rotated all the way to the left the light is in its lowest mode. Rotating the ring to the right increases the brightness levels.

^ Fins on the head help dissipate the heat created by the well driven MT-G2 emitter. The milled scallops in the fins provide anti-rolling when the light is placed on it's side.

^Very mild orange peel (MOP) on the reflector provides a smooth beam spill. The really nice AR coating is visible here as well.

^ The reflector is well shaped and provides excellent output for it's size.

^A better head on look at the reflector and well AR coated lens. It's actually quite pretty! Would make great flashaholic wallpaper. ;)

^ Smooth, anodized threads mate perfectly with the threads on the battery tube and provide an extra level of security by allowing mechanical lockout. The heavy center spring provides low resistance and allows good impact shock protection.

^ A very solid contact plate ensures a lifetime of use with minimal wear. Notice the wet look to the screw heads that secure the contact board to the base of the head? This is because Acebeam puts drops of a clear epoxy over the screw heads to make removing them extremely difficult since the screw driver cannot get into the notches. They can be dig out but not without difficulty. I suppose this is done to discourage modding the driver and to tell if the light was tampered with and thus voiding the warranty. it's still possible to get into the head and mod the driver but it is a PITA to do.

^ A look at the threads on the battery tube and the thick O-ring that seals the joint form water ingress. All threads are properly lubricated.

^ A look at the solid battery carrier. It fits perfectly in the body with minimal rattle.

^There is plenty of space for even the longest of protected 18650 cells. The ones shown are unprotected Panasonics but you can see that there is easily enough room to hold 70-71mm cells.

^ A peek down the battery tube shows the dual contact springs at the base of the K40M.

^ A forward-clicky switch in in the center of the heavy, aluminum tail cap. The switch boot is silicon and has good feel. not overly stuff and not too squishy or delicate feeling. My only complaint with this tail cap is there are no finger scallops in the rim to allow easier clicking of the switch in a tactical hold.

With the tail cap removed you can see how heavy it is. The heavy, unanodized threads allow full conductivity. The switch cap can be swapped easily by simply unthreading the brass retaining ring counter-clcokwise.

^ Here's a look at the threads at the tail of the body tube.

^ The switch PCB is sandwiched between the tail cap and the shelf in the rear of the body tube. Mounted on the outside of the PCB is the switch and several electronic components that help control it.

The inside face of the switch MCB contains the positive and negative contact springs. Note the superb soldering and heavy, gold plated springs.

^ Back at the front of the light, unthreading the deep bezel reveals the reflector which is attached to the inside of the bezel by a threaded ring.

The reflector is machined from aluminum. The bezel threads on the head are anodized, well machined, and lubricated. The thick O-ring prevents the elements from entering the head via the bezel joint.

Here you can see the large 15.8mm wide hole that accommodates the Cree MT-G2 LED.

^ The threads on the inside of the bezel are great. The brass retaining ring that secures the reflector drops over the reflector from the back and sits on a lip machined into the back of the reflector face.

^ A sturdy O-rings sits perfectly into a groove in the back of the bezel face and the thick 69.9mm*3.5mm lens seats against the O-ring. Once the reflector is threaded tightly into the bezel a complte seal is created to resist entry of water or other elements.

^ Looking into the front of the head with the reflector removed shows us the MT-G2 LED and the copper DTP (Direct Thermal Path) MCPCB it is mounted on.

What appears to be 22-24ga wire is soldered perfectly to the contact pads. The copper MCPCB has a smear of thermal paste under it and is secured to the solid emitter shelf with two Phillips screws. A white plastic centering/insulator prevents the reflector from shorting on the MCPCB.


The TN35 and K40M bear more than a striking resemblance to each other especially from the neck down where they are practically identical. In performance they are similar but definitely not identical. When ThruNite came out the TN35 it was an upgrade to the legendary TN31 series. They used the same head and reflector as the TN31 but modified the reflector to accommodate the larger MT-G2 reflector. When Acebeam (then "Supbeam") decided to emulate the existing King of MT-G2 lights, they decided to one up it with a completely redesigned head and a reflector optimized from the start for the MT-G2 LED. Even with the higher output of the K40M I still expected the larger reflector of the TN35 to out throw it especially since indoors on a ceiling the TN35 has a smaller, more focused, and brighter hotspot. Surprisingly the K40M cleans the floor with the TN35 at longer distances. I can only attribute this to the optimized reflector. Both lights are great and being the monstrous fan of ThruNite that I am, I have to admit that Acebeam has outdone them this time as well as made a new fan.

Let's take a quick look at the two lights side-by-side so you can see the obvious differences between them.

^ The larger reflector diameter of the TN35 is readily apparent and contributes halfway to it's narrower spill.

^ Here you can see the difference in depth between the two. Where the TN35 is about as deep as it is wide, the K40M is over square at 69.9mm wide and only 52.4mm deep.

^ Side by side you can see the narrower spill of the TN35 as well as the difference in tint.

^ This gif shows the beams side-by-side at different exposure values to bring out the details not visible with the naked eye.

^ Here I have lined up several lights of competing output and throw levels except for the TK61 on the far left (there just for size reference) and the TK35UE on the far left (a lower output MT-G2 compact light). From left to right they are the Fenix TK61, ThruNite TN35, Acebeam K40M, THruNite TN30, Powertac X3000, and Fenix TK35UE.

^ From left to right: Fenix TK61, ThruNite TN35, Acebeam K40M, THruNite TN30, Powertac X3000, and Fenix TK35UE.

^ You can see the slightly more compact size of the K40M compared to the TN35. This is due to the smaller head and shorter reflector depth.


The K40M is well driven and judging form the output compared to other known lights I would say the MT-G2 is driven at around 6A. Acebeam isn't afraid to push beyond the recommended Cree specifications and that is what makes their lights so appealing to us flashaholics. Combined with reasonable pricing and great build quality they are almost irresistible. OTF lumens are lower than the claimed lumens based on my testing but not by too much. Throw is quite a bit better based on my measurements than what Acebeam claims for the K40M. Once thing for sure, people who discount the MT-G2 emitter as a thrower have never had one of these great lights. Just a year or two ago 530 meters of throw would have planted a light firmly amongst the heavy hitters of throw with only a few rarified and very expensive lights outgunning it.

The Strobe mode cycles between very fast and slower to provide extra confusion to the recipient of it. Frankly 2800 lumens in your face should be plenty to render an attacker completely helpless and ineffective.

The great thing of the K40M, and others with this emitter, is the massive lumen output they are capable of with a single emitter. No more multi-emitter XM-L2 lights to get this amount of light. Just one big reflector with gobs of spill, a large usable hotspot, and better throw than most multi-emitter lights with this amount of output. I will let the numbers speak for themselves.

I measure OTF lumens using my calibrated Integrating Sphere. Output on high is measure at 30s based on ANSI standards. Candelas are measured at 8.89 meters and converted back to 1 meter. Throw distance is calculated to 0.25 lux at 30 seconds, same as ANSI standards.

Finally, let's have a look at some beam shots. These are taken at a distance of 70yds.



  • Excellent build quality and output.
  • Copper MCPCB with Direct Thermal Path
  • Sturdy case and great packaging
  • 5000k tint
  • Good quality holster and nice lanyard
  • Waterproof
  • Good run time
  • Good heat sinking
  • Great moon low
  • Zero detectable PWM in any mode
  • Momentary mode
  • Excellent AR coated lens
  • Better than claimed throw
  • Excellent knurling
  • Excellent laser etching
  • Perfect mode spacing
  • Fits longer protected cells
  • Chamfered lanyard holes in the tail that can fit 550 Paracord.
  • Anti-roll on flat surfaces
  • Tail stands perfectly


  • No thumb cutout in tail cap lip like on X40 model
  • Holster on the large size.
  • Control ring is a touch too stiff.
  • Rated lumens are higher than I see in my testing (not by much though)

With an average street price of roughly $130 USD shipped, the Acebeam K40 is a fantastic light with few rivals at any price. It would make a great light for SAR or for an LEO. Perfect for camping hunting, and hiking, it's the prefect compromise between flood and throw and eliminates the need to carry two or more specialized lights. I highly recommend the Acebeam K40M for any flashaholic and confidently give it my "Mac Approved" rating!

Does it outthrow TN35? Based on your pics - it does.

Thanks for the review!

I just received mine today. Based both on your review and a few minutes of own testing, I'm very happy with it.

..oh, and it has custom engraving too.. ;)

Hey johnnymac,

Thanks for the nice write-up!

Just found a small mistake you made in the comparison shot, you said the fenix is on the far left, but you meant far right?

And I'm a bit surprised you couldn't find more cons. You really couldn't find any?

nice review as always!

could you take some amp measures at the tail?
please add there:

There are two Fenixes :wink:

Thanks for the review mate. I really enjoyed this one

Exactly! :stuck_out_tongue: Tk61 on the far left and the TK35UE onthe far right. Just as it says in both picture descriptions.:smiley:

Whaddya mean? I found four negatives and honestly, aside form them I really can’t find any. This is a great light!

Thanks for the beautiful pics & reviews!

Nice to see it compared to the TN35, thanks. I feel like I’m the only one that is bothered by them incorrectly spelling ‘Standby’ with space…

Nice Review!

Very nice review JM.


The K40M is well driven and judging form the output compared to other known lights I would say the MT-G2 is driven at around 6A.


I posted these numbers in another thread, but for everyone wondering, here is what I measured at the emitter on a stock K40M:

4,86Amp @ startup

4,77 10 sec

4,71 30 sec

4,66 1 min

4,18 1 min 10 sec

4,16 2 min

4,14 2 min 30 sec

4,12 3 min 30 sec

4,11 4 min 30 sec

4,10 5 min

Considering the emitter current, I would say output is very very good thanks to the good reflector, lens and high bin emitter.

On my light it seemed like they had some sort of blue looking loctite on the screws as well. (On my K50M battery carrier screws there were no loctite, just the epoxy) Just a warning that it may be even more of a PITA to get them out compared to what some might think.

Thanks for a great review of a great light JohnnyMac !

Top notch review mate, great work.

Time to pull the trigger

Nice review. Love the pics :smiley:

Thanks JM for the review and nice picture.

In fact when I clicked into this thread I wish I could read more cons of this light so that I wouldn’t be tempted to buy it…

But, damn…

Great review and thank you JohnnyMac. :slight_smile:

Very nice review, JM. Interesting that ChibiM noted more cons. I wonder if the lights are not identical, or if it’s just a matter of different expectations or taste?

Do you owners think the control ring can be operated while wearing gloves?

I received a K40M in a BLF group buy a few weeks back. When I received the light I turned it on and pointed it at the wall about 10 feet away. That’s when I noticed a small hot spot within the usual hot spot. I haven’t had a chance to check it out to see if it’s a focus issue or an artifact from the MT-G2 emitter. Has anyone else experienced this issue? Just curious. Anyways, there is a fellow over on the other forum that has tail caps with cut outs for the thumb. It’s anodization matches well the factory finish and it’s machining is top notch.