Cyansky K3 Tactical Flashlight Review

Cyansky K3 Tactical Flashlight Review

The Cyansky K3 Tactical is a new flashlight by Cyansky offering a dual switch interface, the new Luminus SFT-40-W emitter, and a tactical feature set.  Read on for testing!

Official Specs and Features of the Cyansky K3 Tactical Flashlight

Here’s a link to the Cyansky K3 Tactical flashlight product page.


There is only one version of the Cyansky K3 Tactical flashlight.

Cyansky K3 Tactical Flashlight Price

With cell (as seen in this review) the Cyansky K3 Tactical flashlight costs $84.95.

Short Review

Cyansky fills an interesting market.  They make quality products and seem to be a great up-and-coming brand.  This Cyansky K3 Tactical flashlight is no exception.  This is the first SFT-40-W flashlight I’ve seen, and the performance is quite good.  The Cyansky K3 Tactical offers great build quality, and looks nice too!

Long Review

The Big Table

Cyansky K3
Emitter: Luminus SFT-40-W
Price in USD at publication time: $84.95
Cell: 1×21700
Turbo Runtime Graph High Runtime Graph
LVP? Not really
Switch Type: Both
Quiescent Current (mA):
On-Board Charging? Yes
Charge Port Type: USB-C (On cell)
Charge Graph
Power off Charge Port
Claimed Lumens (lm) 1600
Measured Lumens (at 30s) 1451 (90.7% of claim)^
Candela per Lumen 65.8
Claimed Throw (m) 600
Candela (Calculated) in cd (at 30s) 2820lux @ 5.95m = 99835cd
Throw (Calculated) (m) 631.9 (105.3% of claim)^
All my Cyansky reviews!

^ Measurement disclaimer:  I am an amateur flashlight reviewer.  I don’t have $10,000 or even $1,000 worth of testing equipment.  I test output and such in PVC tubes!!  Please consider claims within 10% of what I measure to be perfectly reasonable (accurate, even).

What’s Included

what's included

  • Cyansky K3 Tactical Flashlight
  • Cyansky 5000mAh 21700
  • Charge cable (USB to USB-C)
  • Spare o-rings (2)
  • Spare switch cover
  • Lanyard
  • Nylon pouch/sleeve
  • Manual

Package and Manual

This nice little note is included on a hang-tag on the light.





Build Quality and Disassembly

feature photo

As I said above, the Cyansky K3 Tactical flashlight is a very well-built light.  Cyansky does this… they build very nice lights!  I’ve reviewed a bunch of them, and even in categories I might not chase, it’s easy to note that the lights are still nice quality.

This is a “tactical” flashlight – though I’m not certain what the qualifiers are for “tactical.”  Strike bezel?  Check.  Dual switch interface?  Check.  Momentary turbo or strobe?  Hold up wait…

Here’s the top-down view.

The head – the biggest diameter part, that is – looks to be removable.  I was unable to unscrew that part, though.

head seam detail

Cyansky touts this bezel as a zirconium bezel.  I don’t doubt that but I do think it’s those little inset balls (the glass breakers) that are zirconium and not the whole crenelated part you can see below.  (In fact I don’t even think that’s a separate part from the head itself).

strike bezel

Below you can see the tailcap removed.  The spring is just a little proud (and that’s fine).  The threads are square-cut, anodized, and lightly lubed.

tailcap threads

Inside the tailcap you can see that the spring is quite long.  The head doesn’t have a spring at all, which doesn’t support the idea that this is a tactical flashlight.  You can correct me if I’m wrong about that!  The idea is that dual springs would keep cell contact during weapon recoil.

head and tail contacts

On the other hand, this tailcap spring is very beefy and might stand up to recoil fine.  I turned on the light and banged it around a bunch and the light stayed on.  But I didn’t test it with recoil.

beefy spring

Size and Comps

Head diameter: 40mm
Body diameter: 25.4mm
Length: 151mm
Weight: 133g (without cell)

If the flashlight will headstand, I’ll show it here (usually the third photo).  If the flashlight will tailstand, I’ll show that here, too (usually the fourth photo).

in hand

Here’s the test light with the venerable Convoy S2+.  Mine’s a custom “baked” edition Nichia 219b triple.  A very nice 18650 light.

And here’s the light beside my custom engraved TorchLAB BOSS 35, an 18350 light.  I reviewed the aluminum version of that light in both 35 and 70 formats.

beside torchlab boss 35

You had to know I’d do this….

joke photo no cell tube

Retention and Carry

You’ll probably notice the pocket clip first, though there are a few options for carry.  The clip is a standard friction fit variety.

This clip fits only on the tail end of the Cyansky K3 Tactical flashlight.

pocket clip hug

Next for carry is the lanyard.  You could likely attach the lanyard on the pocket clip, but I’d go with these two holes on the tail end instead.

lanyard holes

Only one side of the tailcap has this hole set.

other side no lanyard holes

lanyard installed

The lanyard is what I’d probably describe as “nothing special.”  It gets the job done, and is quite lanyard’y, but overall is just a simple piece of cord with an adjuster.

lanyard installed

Finally, there’s this nylon sleeve.  It’s not really a pouch (as I’d say “pouch” implies “closed”).  It’s very suitable for belt attachment and allows easy access when mounted this way.

nylon pouch nylon pouch

Power and Runtime

The Cyansky K3 Tactical flashlight is powered by a single lithium-ion cell.  Cyansky includes an appropriate cell – a 5000mAh 21700, the BL2150U.

included 21700 cell

As far as usage goes, this is a standard button top 21700.  It has some additional features, which I’ll cover below.  This is the same cell that’s used in the other Cyansky 21700 cell lights.  My flat top 21700’s don’t work in the K3!

That said, a button top 18650 will work in a pinch, but it’s loose inside there.  It’s the button that’s important here.  Button top cells will work.  Flat-top cells will not work.

The cell fits into the K3 in the usual way – positive terminal toward the head.

included 21700 cell installed

Here are a couple of runtimes.  There’s a big stepdown at around 1.5 minutes, but then the light holds around 900 lumens for over an hour.

runtime graph

Output on high is flat for over two hours, at around 750 lumens.

runtime graph

In the runtime graphs above, and on bench power, I did not observe low voltage protection.  This is sort of to be expected with a tactical flashlight.  The light steps down to “very low output” at around 2.6V and then finally shuts off (ish) at 2.5V.


As stated, the cell has some other features too.  There’s built-in USB-C charging, by way of a USB-C port on the positive terminal end.

21700 USB-c charge port

Another feature is a little indicating LED right in the positive terminal of the 21700.  When charging, this indicator is red.  When charging is complete, the indicator is green.  Otherwise, the indicator is not on at all.

An appropriate cable is included – USB to USB-C.

Charging proceeds at a fairly slow 1.5A or so, which is well under 0.5C for this 5000mAh cell.  Time required is around 3 hours, and the terminal voltage seems to be consistently 4.19V, a very good termination voltage.

charging graph

Modes and Currents

Mode Mode Claimed Output (lm) Claimed Runtime Measured Lumens Tailcap Amps
Turbo 1600 2h 1451 4.66
High 800 3h 747 1.67
Med 200 12h 0.33
Low 30 100h 0.03

Pulse Width Modulation

No real PWM on any mode.  Low shows some squiggles, which I don’t believe is PWM.

For reference, here’s a baseline shot, with all the room lights off and almost nothing hitting the sensor.  Also, here’s the light with the worst PWM I could find.  I’m adding multiple timescales, so it’ll be easier to compare to the test light.  Unfortunately, the PWM on this light is so bad that it doesn’t even work with my normal scale, with is 50 microseconds (50us).  10ms5ms2ms1ms0.5ms0.2ms.  In a display faster than 0.2ms or so, the on/off cycle is more than one screen, so it’d just (very incorrectly) look like a flat line.  I wrote more about this Ultrafire WF-602C flashlight and explained a little about PWM too.

User Interface and Operation

Two switches are used for control of the Cyansky K3 Tactical flashlight.  First is the mechanical tail clicky.  It’s a forward clicky, which allows momentary actuation.  This switch also serves as a mechanical lockout to prevent any parasitic drain on the cell

mechanical tail switch

mechanical tail switch profile

The switch cover is big but the switch itself is normal-sized.  It’s not terribly thick, so you can feel the actual switch underneath.  The clicky is very clicky and the action is low.

The second option for operation is the e-switch on the side near the head. This switch is metal(ish?) and very proud.  Also, it doesn’t compete with anything else, so it’s very easy to find without looking.  Notably this switch (cover) is improved from lights like the H3, which is otherwise a very similar flashlight.

The user interface is not complicated.

Here’s a UI table!

State Action Result
Off Click Tail Switch (TS) On (last used mode, except strobe)
On Click TS Off
Off Click Side Switch (SS) No action
On Click SS Mode advance L>M>H>T
On Hold SS Strobe
Strobe Click SS Return to the previous mode

For this being billed as a tactical flashlight (and also “looking like one”), it’s surprising that there’s no easy or direct access to turbo or strobe.

LED and Beam

The emitter is a Luminus SFT-40-W. A smooth deep reflector is used here.



The bezel is crenelated, so light will shine out when headstanding (and on).

crenelated bezel

Again, Cyansky bills this bezel as zirconium, but I suspect it’s just those three-strike points that are zirconium.  They aren’t sharp; these are tiny spheres.

reflector detail uncalibrated beam photo

These beamshots are always with the following settings:  f8, ISO100, 0.3s shutter, and manual 5000K exposure.

Tint vs BLF-348 ( 219b version) (affiliate link)

I keep the test flashlight on the left, and the BLF-348 reference flashlight on the right.

I compare everything to the 219b BLF-348 because it’s inexpensive and has the best tint!


What I like

  • Great output
  • Great throw
  • Simple user interface
  • Brand UI consistency
  • Excellent build quality
  • Cell is included
  • No PWM

What I don’t like

  • Cool white
  • No direct access to strobe or turbo
  • Cost is a little high for a new-ish brand


  • This light was provided by Cyansky for review. I was not paid to write this review.
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1 thought on “Cyansky K3 Tactical Flashlight Review”

  1. What do you think of the SFT40? I’m hoping to source some warmer ones for modding. I hear it’s not quite as throwy as the Osram throwers but should have better tint and CRI options available soon.

    Thanks for the review.

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