[Review] Klarus XT21X Pro

We don’t hear often about Klarus here at BLF. So let me show you their XT21X Pro, a 21700 tactical flashlight with dual tailswitch.

Klarus sent me this light for review, thank you very much!

This review is also available in German on my website: https://www.sammyshp.de/betablog/post/131

Supplied parts and hardware

The XT21X Pro comes with several accessories in a nice box with internal compartments.

  • protected 21700 Li-ion battery with 5000 mAh (3.6 V at arrival)
  • holster
  • clip (already attached)
  • lanyard
  • 1x replacement o-ring
  • USB-C charging cable
  • adapter from USB-C to Lightning
  • adapter from USB-C to USB-A
  • 18650 adapter
  • manual (EN, DE, IT, FR, ES, CN)

The flashlight has a total weight of 233 g with its battery. It is 163 mm long and has a diameter of 41 mm (head) and 29 mm (tailcap).

The knurling is somewhat aggressive, but allows a safe grip of the flashlight. Some edges like the “cooling fins” on the head are rather sharp. On some places the black anodization came slightly damaged. (But this flashlight wants to be used, not collected!)

The clip-on clip sits firmly in its groove an appears to be reliable. With a large capacity of 6 mm it fits also on thicker belts.

There are two small holes in the tailcap for a lanyard.

The bezel is made out of blackened stainless steel to protect the light against hard drops and helps with self defence, breaking windows etc. The glass is recessed by about 8 mm.

The battery can be charged internally via a USB-C port which is protected against water by a silicone cover. Charging status is shown with a red/green LED in the switch. Charging runs at about 2 A and terminates at 4.15 V. It took about 3.5 h to fully charge the battery from 3.3 V. During charging the flashlight can be used, but only via the side button.

In the other direction the flashlight can be used as a power bank. This feature isn’t mentioned in the manual and the only indication is a small pictogram on the packaging. It works fine, though.

The flashlight can also be carried in the supplied holster. It includes an eggcup-like part to protect the tailswitch from accidental activation.

It’s a very nice holster out of thick material and a velcro latch. It can be attached via a D-ring, a fixed loop or a velcro loop.

The manufacturer gives the flashlight a rating of IPX8, so it should handle everyday water accidents perfectly fine.

User interface and handling

The special feature of the XT21X Pro is its dual tailswitch in addition to a side button.

The round switch activates turbo. It is a forward clicky, so it can be used for momentary or blinking.

The second button enables strobe. If pressed for less then two seconds, the flashlight will turn off after release. Otherwise strobe stays on. The strobe alternates between 17 and 8 Hz every four seconds.

When the flashlight is on, the second button will toggle though the five brightness levels.

Alternatively all functions are accessible via the side button. A short press turns the flashlight on with the last used brightness. Another press changes the brightness. Double press for strobe and hold for off. Holding from off to reach the lowest level.

Click for on, hold for off always confuses me. I’ll change the brightness instead of switching it off and multiple presses to change the brightness quickly turns on the strobe mode.

Also the flashlight can be switched off only with the button it was switched on. If you used the tailswitch to turn it on, holding the side button does nothing. Have you used the side button, pressing the tailswitch goes to turbo and you have to press it again. (Or just tap it which flashes shortly and then switches the light off.)

You can switch from the “tactical setting” to an “outdoor setting” which changes the behavior of the tailswitch. The primary tailswitch will turn the light on at the last used brightness and the secondary tailswitch can be used to access the lowest level.

Here’s an excerpt from the manual:

You can lock the side button by holding it for five seconds. The flashlight can then be used from the tailswitch exclusively. Press the side button three times to unlock.

The other way around works too: Loosen the tailcap to lock the tailswitch and use the flashlight with the side button. Or lock both at the same time.

I’d wish I could change the button mappings to access momentary turbo with the secondary tailswitch, which returns to the previous brightness. Direct access to strobe is helpful to get attention, but right now the flashlight doesn’t return to the previous brightness (either off or turbo).

I like the handling of the flashlight. While the side button is hard to find by feel as usual, the tailswitch can be accessed immediately.


The XT21X Pro uses a cool white Cree XHP70.2 LED. That’s a very powerful LED that can handle much more current than this light can provide and is very reliable. But it’s not beautiful at all.

The deep orange peel reflector creates a nice intense spot with smooth gradient into the bright spill. You can clearly see the tintshift from green/yellow to magenta/blue.

In total the beam is rather floody with a reach of 336 m (ANSI FL1, which is more like 150 m in reality).

Driver and runtime

The manufacturer specifies the maximum brightness with 4000 lm and a runtime of 2.5 h – but ANSI FL1 again. The definition of runtime is the time above 10% output, rounded to the nearest 15 minutes. In the runtime chart you can see how this looks like in reality:

Too bad that even the second highest level has stepdowns. At least the first 30 minutes are perfectly constant. But nevertheless “maximum 4000 lm” is somehow misleading. The manual says that the flashlight has temperature regulation to prevent overheating.

The five brightness levels are reasonably spaced. “Moonlight” might be the wrong name for the lowest level, but it suits a flashlight of this type.

Mode Brightness (by manufacturer) Current (measured)
Turbo 4400 lm 13.0 A
High 1500 lm 2.15 A
Medium 400 lm 0.60 A
Low 100 lm 0.16 A
Moonlight 5 lm 0.03 A
Off –– 188 µA

The flashlight uses a boost driver which provides constant current to the LED. This allows constant brightness independent of the battery voltage and has no PWM at all.

During the first five seconds an LED in the switch indicates the state of charge of the battery. “Blinking red” means 3.25 V. From that moment the flashlight can only be used in low mode, which still runs for hours. The boost driver could have used the battery much better in my opinion. At 2.7 V the flashlight switches off.

Color State of charge
Green 70 – 100 %
Orange 30 – 70 %
Red 10 – 30 %
Red blinking < 10 %

Both sides have a double spring. At the head there’s also a circular spring contact – maybe for a proprietary battery that has both poles at the same side?

Implementation of the dual tailswitch is very interesting. Although it has a mechanical switch, it’s used only for signaling through an inner tube, while the current runs through the flashlight body itself. Each switch has its own resistor (3.4 kΩ and 2 kΩ) which allows the driver to detect which button is pressed.


You can feel that the Klarus XT21X Pro is made for duty. Tough, functional, a workhorse. Maybe not so well suited for EDC because of its size.

I really like the dual tailswitch, but would like more flexibility to change the functions of each button.

Klarus XT21X Pro at klaruslight.com

Have to run it at the 400 lumen setting to get constant current light. Plus, tint shift is super yellow due to the lack of throw (wrong emitter for this light). A terrible offering.

Good review.

I think I will do a (partial) runtime measurement for the 400 lm level. A boost driver has so much potential, yet they decided to step down early.

Honestly I’ve never seen a XHP70.2 without tintshift. It’s a very nice LED for high power, but ran at lower power in this light. Due to its size you won’t get much trow without a very large reflector. I think the color would improve with d-c-fix, but that would make it even more floody.

I can’t say I know much about this particular Klarus but overall the brand is solid.

Yes, but to this level the shift is crazy because the reflector just isn’t right IMHO.

I think it’s more a property of the combination of a (large) flip chip LED with any reflector.

Here is an example of the Sofirn SP33S, also XHP70.2:

Nice review, thanks.

400 lm is rediculous for a 21700 XHP70 light. What were they thinking?

Maybe something like: “Who needs constant output on high (”1500 lm”) for more than 30 minutes – did they forget to turn it off? Better step down for a longer runtime.” I guess you can step up again after the 30 minutes, but I’ll have to check. Currently I’m running the “400 lm” test for four hours.

Yeah… for three hours. Battery was still at 3.7 V :person_facepalming:

I was just offered to review this model and I don’t think it’s a massive deal since you can just easily reactivate the mode. I see many tactical models that have only two levels, a low and the turbo. I do agree there shouldn’t be a timer, but a deal breaker?