This is something a bit different: an infrared (IR) flashlight from Cyansky. The K3-I8 is very similar to their K3 tactical light but with a high power IR emitter instead of a normal white LED. Note that the model name is with the letter I, not number 1: K3-I8, not K3-18.

You can buy the Cyansky K3-I8 flashlight directly from Cyansky.

A bit about night vision

Infrared light has a wavelength above 700 nm and can’t be seen by human eyes. That means you need special night vision equipment to be able to see it. Night Vision Goggles (NVGs) or Night Vision Devices (NVDs) in general allow you to see in the dark without others seeing you. NVGs are used by law enforcement, military and hunters.

Most NVGs use active illumination, where they shine an invisible IR light source to light up an area.

Night vision goggles

IR is also used by night vision cameras and baby monitors. These often come with weak IR LEDs, so the Cyansky K3-i8 can be used to extend the range of these.


LEDOsram IR 850nm

What’s in the box?

I received a pre-release version of the Cyansky K3-iR, so the final packaging might be different. Generally Cyansky’s flashlights come in a high quality cardboard box, with specs printed on the outside.

In the box

  • Cyansky K3-i8 IR flashlight
  • 21700 cell
  • USB-C charging cable
  • Lanyard
  • Pocket clip
  • Spare tail switch boot
  • Nylon holster
  • Warranty card

The final package will include a manual too.

Cyansky also sells accessories such as a figure 8 clamp and a remote switch for most of their lights.


Size and everyday use

Dimensions148.6mm long x 40mm head and 25.6mm body
Weight with cell120g

The K3-i8 is a fairly standard size for a tactical light, with a slightly flared head. The 40mm head won’t easily fit in a small trouser pocket but will slip into a larger one or a jacket just fine. The pocket clip is very solid and has a tight fit. The lanyard pouch is a nice addition: it has a belt loop and velcro that allows easy carry with quick access.

There’s no fins for heat dissipation but these aren’t really needed with the power the K3-I8 draws. The head has slight crenelations.

On to the switch, this is a standard tail switch with rubber boot. The switch is mechanical and forward clicky. This means you can half press it to turn the light on.

Quality and Insides

The light feels solid and well built, with slightly shiny anodising. The body tube has fairly aggressive knurling that makes the light easy to grip. If this was an EDC flashlight then the knurling would be a bit much but as a tactical light it’s well placed.

Opening it up you’ll see Cyansky’s usual high build quality. The threads are well lubed and square cut. The threads on the body tube are actually anodised at both ends, allowing the tube to be revered, which means the clip can go either way round.

Both ends have a brass spring. The tail one is fairly long but this is fine for the low current required by the LED.

The bezel didn’t seem to unscrew to access the LED or driver. It seems like Cyansky has glued it to keep it all in one piece.

Cyansky rate the flashlight as IPX8 waterproof and it should be submersible to 2m underwater for a short period. It’s also 2 meters impact resistance and rated to work in environments from -30℃ to 50℃.


Normally I talk about tint and colour temperature here. All I can say about this light’s LED is that it’s an IR Osram SFH 4770S LED that outputs primarily at a wavelength of 850nm.

Anything over about 700nm is classed as infrared, with 850nm being the standard for most IR devices. This falls in the CIE IR-A range and the ISO 20473 Near-Infrared (NIR).

The IR LED is rectangular and looks to have a very small light emitting surface (LES). The LED itself looks to be 2030 footprint but the LES is about 1mm2. This, combined with the smooth reflector means the light gives lots of throw.

One handy thing is that the light gives off just a fraction of a lumen of visible red light. This means you can see whether the light is on or off. Note that for tactical use, this very dim visible light could give away your location if someone looked directly at it.

Make sure to double check the light is off when you’re done with it as a couple of times I left it on accidentally. If you’re putting it away for storage then the best option is to unscrew the tail cap slightly.


I don’t have any other IR lights but here’s a size comparison with other tactical lights. From left to right:

  • Cyansky H3
  • Armytek Viking Pro
  • Cyansky K3-I8
  • Armytek Dobermann Pro
  • Cyansky P25
  • Cyansky P20

User Interface

Click on, click off, half press for momentary.

That’s it with the K3-IR. The only modes are on and off. 

Cell and charging

Cyansky provides a 21700 size cell (battery) with the light. This is rated at 5000mAh. It’s 77.0mm long, so won’t fit in many standard chargers.

Fortunately the cell has built-in USB-C charging. This took up to 1.4V from a USB source and also works fine with a C-to-C cable. The cell has a red indicator light when charging, which goes green when fully charged. Full charging will take 3 or 4 hours and the cell measured a healthy 4.18V when it stopped charging.

Other flat top 21700 cells won’t work in the light but longer button top cells should. Longer button top 18650 cells should work too, though I’d recommend sticking to button top 21700 cells.


There’s no lumens to measure here, so my normal integrating sphere is no use.

Checking the current draw with a clamp meter, the light drew 1.52A from the cell. This is just over 6W of input, so I expect Cyansky’s listing of 5W for the LED output to be correct.

Cyansky has rated the light as having 350 meters throw. I’m not sure what this number is referring to as normal ANSI throw is a measure of lux (visible light).


At around 1.5A current from a 5000mAh cell we should expect just over 3 hours of run time.

Cyansky has a runtime graph which shows output dropping to about 50% in 3 hours.

Cyansky runtime specs

I couldn’t check this accurately but leaving the light on and checking periodically showed it getting very low at 5 hours.

Cyansky could have given the light a high and low mode to get more than 3 hours of runtime but given that this is an IR light I think they made the right choice to keep it simple.


Unfortunately I don’t have any proper night vision devices to put the light through its paces.

I do, however, have an IR security camera with IR sensor. The camera has its own IR LEDs but these aren’t very bright.

You can see here that the flashlight lights up the building at 85m away easily. With a proper night vision camera camera (especially with magnification) I’d expect the Cyansky K3-I8 to light up targets well over 100m and likely further.

Use the slider control to see the image with and without the flashlight. Thanks to Grizzly’s Reviews for this idea. I’ve added distances to the spot in red.


With the simple user interface and good build quality, you can’t really go wrong with the Cyansky K3-I8 IR flashlight.

From my tests it throws the IR light quite a distance: I can easily over see 85m with my camera. This means you can see things with an IR camera at a much greater distance than any built in LEDs.

You can buy the Cyansky K3-I8 flashlight directly from Cyansky. They also have a Thanksgiving sale at the moment, which gives 10% or 20% discount off most of their lights and ends on 27th November.

This pre-release flashlight was sent to me for review at no cost by Cyansky.

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