Klarus XT21C Tactical Flashlight Review

Klarus XT21C Tactical Flashlight Review

Klarus has released the XT21C, a tactical flashlight featuring an included 21700 cell, dual switch interface, and great throw! Read on!

Official Specs and Features

Here’s a link to the Klarus XT21C tactical flashlight product page.


There is only one version of the XT21C.


Klarus sells the XT21C tactical flashlight for $104.95.  This price includes the 21700 cell, too.

Short Review

Tactical flashlights aren’t foreign to Klarus. This one is well refined and I’d say meets the needs of a tactical flashlight user.  The mode order from highest to lowest, while maybe not suited to EDC roles, is great as a tactical light.  Output is very high.  Throw is very long.   All in all, this is a solid offering.

Long Review

The Big Table

Klarus XT21C Tactical Flashlight
Emitter: Luminus SST-70
Price in USD at publication time: $104.95
Cell: 1×21700
High Runtime Graph Medium Runtime Graph
LVP? Yes
Switch Type: Both
Quiescent Current (mA): ?
On-Board Charging? Yes
Charge Port Type: USB-C
Charge Graph
Power off Charge Port
Claimed Lumens (lm) 3200
Measured Lumens (at 30s) 2544 (79.5% of claim)^
Candela per Lumen 14.4
Claimed Throw (m) 324
Candela (Calculated) in cd (at 30s) 1135lux @ 4.705m = 25126cd
Throw (Calculated) (m) 317.0 (97.8% of claim)^
Claimed CCT
Measured CCT Range (K) 5600-6100 Kelvin
Item provided for review by: Klarus
All my Klarus reviews!

^ Measurement disclaimer:  Testing flashlights is my hobby. I use hobbyist-level equipment for testing, including some I made myself. Try not to get buried in the details of manufacturer specifications versus measurements recorded here; A certain amount of difference (say, 10 or 15%) is perfectly reasonable.

What’s Included

Klarus XT21C tactical flashlight what's included

  • Klarus XT21C tactical flashlight
  • Nylon holster
  • Klarus 5000mAh 21700 (customized)
  • Charging cable (USB to USB-C)
  • Lanyard
  • Spare o-ring
  • Manual

Package and Manual

Klarus XT21C tactical flashlight box

Klarus XT21C tactical flashlight manual

Build Quality and Disassembly

Klarus XT21C tactical flashlight

I said above that there’s just one version of the XT21C.  That’s true.  However, there are also very similar lights by Klarus.  I’ve tested a couple.  The Klarus XT2CR Pro is very similar.  The Klarus XT11GT Pro is even more similar.

In fact, aside from the different emitter and cell size, I’d say the XT21C is an update to the XT11GT Pro.  Nothing wrong with that – the XT11GT Pro was a good light.

The threads on the tailcap are square-cut and anodized, and not too long.  The walls feel a bit thinner in this section, but I think it’s just this section – farther down the barrel I believe they are thicker.

Klarus XT21C tactical flashlight tailcap off Klarus XT21C tactical flashlight tailcap spring

There are springs on the head and tail, as there should be on a tactical light.  The extra on the tailcap has to do with the dual switches.

Klarus XT21C tactical flashlight spring in head

Size and Comps

35mm x 25.4mm x 146.5mm
Weight: 109.8g 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).

Klarus XT21C tactical flashlight 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.

Klarus XT21C tactical flashlight beside torchlab boss 35

Retention and Carry

There’s a pocket clip included and attached.  It’s a friction fit clip and lives on the tail end only.  For belt carry it’s sufficient.

Klarus XT21C tactical flashlight pocket clip

The included lanyard could attach to the clip in the holes seen above, or in this hole on the tailcap.  The tailcap will be much more secure.

Klarus XT21C tactical flashlight lanyard hole

A nylon pouch is included.  The carry is bezel-up only, and there aren’t any holes for in-holster use.

Klarus XT21C tactical flashlight nylon holster Klarus XT21C tactical flashlight nylon holster

Klarus XT21C tactical flashlight nylon holster


Klarus XT21C tactical flashlight lanyard installed Klarus XT21C tactical flashlight lanyard installed

Power and Runtime

The Klarus XT21C tactical flashlight runs on a single lithium-ion cell.  The required type cell is included at the purchase price, too.  This is a 5000mAh 21700 cell.

Klarus XT21C tactical flashlight with included cell Klarus XT21C tactical flashlight 21700 cell

The cell isn’t quite standard, though.  It has this positive/negative terminal on one end.  This is required for operation of the XT21C, unfortunately.

Klarus XT21C tactical flashlight 21700 cell

Here you can better see the protective shroud around the positive connection.  This will prevent charging the 21700 in a bay-style charger.

Klarus XT21C tactical flashlight 21700 cell

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

Klarus XT21C tactical flashlight 21700 cell installed

Here are a couple of runtime graphs.

Klarus XT21C tactical flashlight runtime graph Klarus XT21C tactical flashlight runtime graph

I observe (and the manual states) the light only switches down to a very low output when the cell voltage is low.  The output is very low – not usable tactically, but certainly enough to find another cell or whatever.

There’s an indicator in the head of the flashlight, too.  This indicator will light up for 5 seconds after the light is turned on.  It indicates as follows:

Green: 70-100% capacity remaining
Orange: 30-70% capacity remaining
Red: <30% capacity remaining
Red flashing: <10% capacity remaining


The Klarus XT21C tactical flashlight has built-in charging.  The charge port is USB-C and has a snug press-in cover.

A USB to USB-C cable is included.

Klarus XT21C tactical flashlight charging indicator

Here’s one charge test.  Fairly standard fare here, with the charge essentially ending around 190 minutes.

Klarus XT21C tactical flashlight charging graph

During charging, the indicator in the head is red.  When the indicator is green, charging is completed.  If the indicator is yellow, something is wrong.

Modes and Currents

Mode Mode Claimed Output (lm) Claimed Runtime Measured Lumens Tailcap Amps
High 3200/800 3m/4h 2544
Medium 400 7h 448
Low 100 20h 112
Moon 5 240h 4.3

Pulse Width Modulation

Here, as below, the mode order is represented:  the graphs from left to right are in descending brightness.

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, which 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

There are two switches on the Klarus XT21C tactical flashlight.  As this is a tactical-use light, the switches are both on the tailcap.

Klarus XT21C tactical flashlight switches

One’s a paddle switch, and one is a mechanical clicky.  It’s a fairly standard tactical setup.

Klarus XT21C tactical flashlight switches Klarus XT21C tactical flashlight switches

There are technically two mode groups.  As shipped (and tested here), the light is in the “Tactical Setting.”  Also available is the “Outdoor Setting.”  The manual states that the default is Tactical.  The other is Outdoor.  Mine actually shipped in Outdoor.  Switch between the two as follows:

From off, hold the paddle switch (“Mode”) until the indicator switch goes from green to red/green flashing.  Then tap the Primary switch.  You can release or leave the light on; the group is changed.

This user interface is just like the Klarus XT11GT Pro, which I reviewed.

Here’s a UI table for Tactical mode.

State Action Result
Off Click Primary Switch High
Off Tap Primary Switch Momentary High
Off Hold Paddle Switch (Mode Switch) Strobe
Off Tap Mode Switch Momentary Strobe
On Click Mode Switch Mode advance (HML Moon)
On Click Primary Switch Off

Here’s a UI table for Outdoor mode.

State Action Result
Any Click Primary Switch High
Any Tap Primary Switch Momentary High
Off Tap Paddle Switch (Mode Switch) Momentary Moon
Off Hold Paddle Switch (Mode Switch) (~1s) Moon
On from Mode Switch Click Mode Switch Mode advance (High Moon Low Medium)
On from Primary Switch Click Mode Switch Mode advance (High Moon Low Medium)
On Click Primary Switch Off
On Hold Mode Switch SOS

LED and Beam

The emitter of choice for this light is a Luminus SST-70.  The emitter benefits from a lightly orange peeled and deep reflector.  Klarus doesn’t state the CCT of this emitter as far as I can see, but it wouldn’t be a surprise for it to be cool white.

Klarus XT21C tactical flashlight emitter

The bezel does unscrew readily.

Klarus XT21C tactical flashlight reflector

The bezel is somewhat aggressive, and as such allows light to shine out when headstanding.

Klarus XT21C tactical flashlight bezel Klarus XT21C tactical flashlight beamshot

LED Color Report (CRI and CCT)

Even on the highest setting, we’re only seeing around 6200K, which isn’t really all that terrible, particularly given that this is a tactical light.  On the lower modes, we’re seeing well under 6000K.  That’s great!  The CRI is not high, but also not a surprise for it to be around 70.


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

Tint vs BLF-348 (KillzoneFlashlights.com 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 KillzoneFlashlights.com 219b BLF-348 because it’s inexpensive and has the best tint!


What I like

  • Complete package
  • USB-C Charging
  • Interface which allows choice (specifically the Turbo to Low direction option in the Outdoor group, which is unusual)
  • No PWM
  • Lower modes are under 6000K, which is perfectly great.
  • Really nice build quality (and feels important in hand)
  • Updated user interface with good moonlight access in the Outdoor Setting

What I don’t like

  • USB-C charging could be considered slow at 1.1A.  The cell could handle much more, and USB-C could too.
  • Cool white emitter
  • Customized 21700 cell.  Despite this becoming standard, I don’t like it.  (However, with the charging setup, I do sort of get it, and the cell is included.)
  • Price – at $105, this isn’t an inexpensive light.


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