AceBeam K40M MT-G2/3*18650 Flashlight

AceBeam K40M MT-G2/3*18650 Flashlight

My new wallpaper! :D

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 Tail cap gummi; 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

^ 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 mile 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

^ 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

^ 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 half way 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!

Post your questions and comments in the review thread on TFF! 😉

7 thoughts on “AceBeam K40M MT-G2/3*18650 Flashlight

  1. Pingback: Acebeam K40M MT-G2/3*18650 flashlight | Johnny Mac Reviews

  2. Fantastic light and yep at $130 it really is a good deal. I like the MT-G2, except for all the heat and the artifacts in the beams with a smooth reflector. I’m glad to see that this one does come with the OP reflector. They all should IMHO. They really do need that extra texture to smooth out those artifacts.

    I might have to pick one of these up someday. Problem is that I am a modding nut and they haven’t left me anything to fix on this one!

    Great review as always.

  3. Pingback: Supbeam K40 V2 MT-G2 - Seite 20

    • Unfortunately I don’t have an X40 to compare to but the X40 is very similar to the ThruNite TN30 which I do have. The TN30 kicks out 3000-3200 OTF lumens so it’s far brighter and it has a surprising amount of throw as well. For throw I’d imagine they are pretty close. If you are a tint snob you will definitely want the K40M. The MT-G2 is an outstanding emitter! Given the choice between the two lights I think I’d take the K40M over the X40 as the better overall light. But again, that’s just my opinion. 😉

  4. Did you mix the flashlights when you compared tn35 vs k40m on wall because tn35 seems brighter when you say it’s not. Sometimes the spill seems smaller on k40m

    • I’m not sure what you are looking at but the outdoor beamshot of the K40 looks far brighter than that of the TN35, at least on any monitor or device I look at the pics on. The center beam is smaller on the TN35 but the centerbeam of the K40M is way brighter. Even the spill looks brighter on the K40 pic to me.

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