[candle lamp]

Supbeam have lately changed their name to Acebeam. The K40 was a high-output XM-L U2 thrower runs on 3x18650 batteries from Supbeam.

K40M is a new MT-G2 class light from Acebeam, updated K40, features a similar build.









Packaging is a nice metal box with built-in packaging foam. Included inside are the light, user manual, warranty card, extra o-rings, spare tailcap boot cover, lanyard, belt pouch.
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Manufacturer Specifications from AceBeam website & user manual :
• 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 : 509 meters
• Peak beam intensity : 65000 cd
• Impact resistant : 1.2 meters
• 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
• 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



Notice : The above mentioned parameters (tested with three 2600mAh batteries) are approximate and may vary between flashlights, batteries, and environments.
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As before, anodizing is a matte black finish (type III), with no chips or damage on my sample. All letterings are clear, bright white. There is a mark (▼) on the control ring that lines up with the labels on the head. The manufacturer, model name, are on the battery tube. The knurling is present over battery tube.
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The light has mainly 2 parts (i.e. head and battery tube) There is a battery carrier in the tube.
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The head appear to be unchanged from the K40 although I note the MT-G2 specification specify the q0 output bin.
The light has a scalloped bezel, and it was not glued down. There is a waterproof o-ring between the bezel insude and reflector. There are two shallow and three deep cooling fins on the head. The head base of the light has a central positive spring to contact with the positive terminal of the battery carrier. The very wide negative contact rim surround the central positive contact spring. The positive contact spring is well isolated from the negative contact rim by the black small plastic insulator.
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The light uses a nice AR coating lens (with 98.3% light transmittance), and the purple hue is reflected on it. The reflector is not as perfectly super smooth as a mirror, unlike the K40. It does seem like it is a very super light OP. The K40M uses a MT-G2 q0 emitter, it's well centered in the bottom of the reflector cup. Even though the light has a large MT-G2 emitter, I would expect reasonably good throw because of the large and deep smooth reflector. I couldn't find the q0 output bin information in the Cree MT-G2 specification sheet and didn't know what tint bin is used for the K40M. Acebeam reports this light has a higher q0 output bin than p0 and neutral white (5000 K) tint bin. The q0 bin gives 2286 lumens and p0 bin 2126 lumens at 3A current.
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There is a control ring, located below the cooling fins. All six constant output switching along with Standby and Strobe are controlled entirely by the control ring. The light has ten slight indents on the control ring to help with feel. There is a label mark (▼) on the control ring that lines up with the labels on the head. The individual six constant output levels are not labeled on the head, but there is a graded output arrow (◢) which shows the direction of the output levels (from max. to min. output). There are firm detents at each level, with a slight click. So you may need to count detents to figure out what output level you are set to.
Like the K40, the total traverse of the control ring is around 165 degrees of the light. The control ring action feels almost the same as the K40. The difference is that I find the control ring to be a bit stiffer but more quiet overall on the K40M. But like the K40, there are firm and clear detents for each level.
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The light uses a metal battery carrier that has 3x18650 cells in series. It looks sturdy and well-made. The carrier has identical central positive contact point isolated by a black plastic insulator and outer negative contact rim at both ends. The positive contact plate is slightly raised, and the negative contact spring has good elasticity in the battery carrier. So all types (i.e., true flat-tops, wide and button-tops) of 18650's work fine. Longer cells may be somewhat tight, but all my protected high capacity (2600~3100mAh) cells fit. You can insert the battery carrier either orientation into the battery tube (i.e., it's reversible), because it has same ends with positive and negative connection terminals. But you should be careful to insert the 18650's into the battery carrier in the correct polarity.
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You can see the fully loaded battery carrier with unprotected & protected cells. I don't have any issue to insert my shortest & longest 18650 cells into the carrier. But the positive contact plate may catch on the heatshrink on the flat cells during removal. So you need to first depress the cells towards the negative spring before removal. The battery carrier introduces little rattle if you shake the light laterally when it's fully loaded with 18650's unprotected . But no rattle with the protected 18650 cells installed in my sample. Note that only 3x18650 li-ion cells can be used in the light (i.e., it doesn't support multiple CR123A or RCR123A due to 4~13V working voltage range).
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Screw threads are triangular cut, but seems good quality. They came well greased. Note that both male & female threads on the head & tube are anodized for head lock-out. They are smooth with no cross-threading or squeaking on my sample.
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Like the K40, the battery tube continues the cylindrical shape with four flat, long rectangular surfaces. The diamond-shaped knurling is presented over most of the battery tube except rectangular sides, and it's a bit aggressive on the handle, helping with grip.
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The switch is the forward click switch which allows the light to be momentarily activated by half-pressing the switch while not affective the mode changing which is completely controlled by the control ring on the head. The switching travel is slightly longer than average, with average resistance and provides audible click when engaged. There are machined indents similar to the ones on the control ring. The switch cap sits recessed within the tail end which allows the light tailstand perfectly. There is no cut-out facilitate easily access to the switch. It's a bit difficult to access it with my medium-sized hands and I have to hold the light further back. There are a couple of holes at the rear end for lanyard attachment.
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There is dual springs (i.e., inner & outer springs) in the battery tube base. The negative current path is carried from the negative contact rim on the battery carrier, carried through the outer spring in the tailcap and the battery tube of the light. Note that Another current does flow from the central positive contact point on the battery carrier to the inner spring in the tailcap.
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The tailcap is screwed to the battery tube together, and it can be removed from the tube without any tools. You will see the mechanical tail switch with an electronic circuit. This circuit can carry the current by 5A. In case of using a simple mechanical on-off switch, it can't accept 5A current (i.e., it may be short-lived). There is an o-ring at the tail threads as well. The light can tailstand stably without the lanyard attached, thanks to the flat base.
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From left to right, VicLite 18650 protected, OHLED Combat Double (Nova MM15), Fenix TK35 UE, Thrunite TN30, Supbeam K40, Acebeam K40M, Fenix TK75 (for size comparison).
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The head size & light weight excluding battery of four lights are as follows (for beamshot comparison):
Combat double (Nova MM15) - 63.7mm / 332g (excluding the handle), TK35 UE - 51.7mm / 272g, K40 - 76.5mm / 505g, K40M - 76.2mm / 497g
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The light is a good size with a right weight to manage for 3x18650 class. The operating the control ring with two fingers (i.e., thumb and index finger) is not difficult, but difficult with the thumb only. The gripability seems good. Handling & balance of the light is good. The overall build quality is very high.
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K40M comes with a nice nylon belt pouch with a velcro strap on the head. The light fits in the pouch head-up only.
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Measured Dimensions & Weight

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User Interface
On-off is controlled by the tailcap forward switch and output switching is controlled by the control ring in the head. Turn the light on-off by the tailcap clicky – press for momentary, press and release (i.e., click) for constant on.

There are six constant output levels, stanby, and strobe. Change output modes by turning the control ring in the head. Arranged from left to right (with the head facing forward) in the following order. L1 (min. output) --> L2 --> L3 --> L4 --> L5 --> L6 (max. output) --> standby --> strobe.
No light is produced on standby, but a small current will be drawn to allow to respond to the control ring turn and for the tail switch assistance as described below.
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Standby Current Drain
Due to the control ring and electronic tail switch, the light has a small current when fully connected and control ring arrow is pointing at standby mode and the tailcap switch is clicked on.
I measured this current at the head as 60.2μA and at the tailcap as 12.6μA with 3xVicLite 18650 (2600mAh) cells. There is no current draw when the tailcap switch turned off as expected. Since the cells are arranged in series for 3x18650, that would translate into around 4 years before the cells would be fully drained. Note that total standby current drain (72.8μA) is slightly higher than 65uA standby current listed in the manual, but this is quite reasonable for a standby current, not a concern. If you want to break this current, store the light locked-out by loosening the head or turn the light off by the tailcap switch when not in use.
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PWM


The light shows no sign of PWM at any output levels. I think the light is actually current-controlled. I notice there is no buzzing sound at all output levels in my sample.
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Runtime

1. Fan Cooling


Runtime performance and output are very good and flat regulation is evident on L6. The light settles around the 83% output mark after 10 minutes runtime under cooling fan. Also I got flat regulation after a minor drop (~5%) on L5 as well. There is neither timed nor thermal-controlled step-down. I expect excellent flat regulation on the other output levels (L1~L4).
Unlike the K40, I couldn't see the light dropped down to a very low output mode similar to very lower Low (L1), instead of completely shutting off when the battery protection circuit was reached. It didn't flicker shortly three times every 25 seconds at a very lower Low output for low battery warning.
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2. Comparison with multi-18650 lights under fan cooling

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3. No Cooling


I measured the surface temp. with thermal probes attached to the light for the no cooling run. The room temp. was 27.2~27.8 degrees, and window was ajar on the test room. The resting temp. for K40M was 29 degrees. You can see the two points on the light where the thermal probes were set in pace as illustrated above for no fan cooling run.
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Note that left y-axis is the relative output. The black and brown lines represent surface temperatures of the light in degrees centigrade (celsius) should be read off the right y-axis.
Like the K40, you will see some gradual drop in output over time. But the temperature continued to rise steeply in the course of the max. output (L6) run, reaching a max. 65.8 degrees at the points P1 after only 17.5 mins running time. The light gets quite hot on L6 about ten minutes later. I stopped the runtime test under no cooling after 17.5 mins, but I assume that the surface temp. will steadily rise while the light is being turned on. I recommend you use not for extended periods and should manually throttle down the max. output level (L6) if you find the light is getting hot to hold.
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Beamshot

1. White door beamshot (50cm) on max. output
- ISO100, F/10.0, 1/250sec, Auto white balance


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- ISO100, F/10.0, 1/400sec, Auto white balance


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- ISO100, F/10.0, 1/800sec, Auto white balance



The overall beam profile is clean. The medium sized hotspot is well focused and a soft corona surrounds the bright hotspot. The spill beam is a bit wide and clean with no noticeable artifact. The tint is a neutral tint. The color temperature (K) seems to be a bit lower than Nova MM15 and TK35 UE in my view.
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2. Indoor Beamshot about 7.0m from the target on Max. output
- ISO100, F/2.8, 1sec, Auto white balance

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3. 55m Outdoor Beamshot on Max. output
- ISO100, F/2.8, 1sec, Auto white balance

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4. 65m Outdoor Beamshot
- ISO100, F/2.8, 1sec, Auto white balance

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The K40M is an impressive thrower with good sized hotspot and spill beam in real life. The hotspot is decent, yet in harmony with the spill.
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The above is the Min. output (L1) showing a characteristic of the Cree MT-G2 emitter. This emitter is one of the directional LED arrays and there are 72 numbers of the chips.
The K40M gives a lower Low output level.

Acebeam K40M was provided by Acebeam for review.