Fenix TK21R

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Fenix TK21R Specifications & measurements

Brand & Model	Fenix TK21R
Flashlight category	Tactical flashlight / Duty
Battery config.	1*21700
Switch type	Rear
Dimensions:
Length	159 mm
Head diameter	36 mm
Weight with battery	225 g
LED & Beam
LED type	Luminus SFT-90
High CRI	No
Focusable beam	No
Features
Onboard charging	Yes
Power bank	No
Specifications and measurements
Specified output	3,600 lm
Measured output (30sec)	3,212 lm
Max. measured output	3,723 lm
Specified beam distance	480 m
Measured beam distance (30sec)	477 m
Specified beam intensity	58,000 cd
Measured beam intensity (30sec)	57,025 cd
Overall rating	4.5 Stars
Review publication date	August 2025

Before we dive in today, let’s go back a ways. The year is 2016. COVID wasn’t an acronym, I celebrated my 6th wedding anniversary, rent was affordable, you could still get two Big Macs for $5.00, and an Extra Value Meal was a good value. That same year, Fenix Lighting Co launched their new, redesigned TK20R flashlight.

For its day, it was slick: Micro USB charging, Cree XP-L HI V3 with 1,000 Lumens, and a dual-switch UI. However, it’s not 2016 anymore and things have changed in the flashlight ecosystem. Fenix has kept up though, launching the upgraded TK20R V2 in 2022, followed by the UE edition in 2023.

Now we have a new addition to the TK family, the TK21R. It’s not entirely new, and roughly based on the TK17 with some tweaks and additions like onboard charging and a different LED. I’m particularly chuffed about that last feature, and I really liked the TK20R V2 I reviewed, so hopefully it’s more of the same, but better.

What’s in the package

Fenix lights come in retail-ready packaging with hang tags and flashy graphics. The TK17 box is Fenix-centric with the orange-black color scheme full of feature blurbs and specs. Inside it’s been redesigned. Gone is the molded plastic carrier and in with a more eco-friendly cardboard carrier with the bits housed in two compartments on the sides.

I like this much better than the old style, because even with the ‘flap’ on the bottom the last TK series I reviewed had, still liked to dump the contents out the bottom when removing it. Out back, you get the spec table and more technobabble. Here’s what’s inside:

• Fenix TK21R
• Fenix ARB-L21-6000B 21700 (loaded in the light)
• O-rings
• Holster
• Lanyard
• USB A to C cable
• Manual
• Warranty and promotional materials

In proper working-light fashion, the TK21R comes with absolutely everything needed to get running. The cell was sitting at 3.7 volts for storage, and I’m glad to see USB cables included (two, no less) and a holster. Remove the isolator, replace the tailcap, and away you go. The cell was charged enough for near-max brightness, but it needs to be fully charged before going to work.

The TK21R belongs to the T series flashlights. These are tactical or duty lights designed for users who need something brighter and more robust than a PD or E-series light. These lights have very simple UIs, springs for driver and tail, and beefed-up bezels for smashing stuff.

They are also weapon-mountable and compatible with a large variety of Fenix accessories like the ALG M-LOK and Picatinny weapon mounts, AER remote switch, ALB bike mount, ALD helmet-mount holder, ALR grip ring, ALP holsters, and the AOT-04 traffic wand. 

The TK21R follows the basic form factor of the TK20R V2. You still get a one-way detachable (friction fit) PVD (with titanium) coated stainless pocket clip and lanyard holes in the tail for retention. The most obvious changes are to the outside: There’s a new slant-cut groove grip pattern similar to the TK17.

I like it, and it adds appreciable traction over the standard straight cut reeding on the TK20R V2. The onboard charging arrangement is similar to the TK20R V2 also, consisting of a collar that unscrews to expose the USB C charge port and charging/on state status LED.

The spiral cut pattern is present on the collar too, and that’s good because on my sample, it was a bit stiff to start due to the tight o-rings and precisely machined threads. This traction also augments the already sound handling manners. It’s nicely balanced, easy to grip, and the controls are easy to access in all grip positions like all the dual-switch TK series lights.

The switchgear arrangement is the same as the TK20R V2: A large forward clicky known as the tactical switch and a momentary e-switch for mode changes (the functional switch). Both have proud rubber boots and are easy to find by feel. This design is similar to Acebeam’s on the P17 and P18.

The main clicky switch (the Tactical switch) has been refreshed and features the silent activation like on the TK17. In all honesty, it’s not my favorite and I’d preferred that Fenix left it alone. It feels okay, and does switch things, but it’s mushy and vague, a bit like a Glock trigger with a good bit of takeup before the ‘wall’ and then the ‘click.’

It almost feels like Olight’s dual position e-switch on the Warrior series, but not as good. I prefer a tactile, snappy mechanical click over this for more positive control. Not that the new one’s bad-it’s just may take some getting used to. The smaller e-switch is also present on the TK20R V2 and controls mode changes and the instant Strobe.

For build quality, Fenix falls between Olight and Streamlight as an uplevel brand, and the dozen or so Fenix lights I’ve tested over the last four years have been exemplary in fit, and finish. Pricing for the TK21R is very reasonable with an MSRP of $176, although it’s often discounted to around $135 US. That’s a great deal for a professional-grade light and competitive with Olight’s Warrior X4 and Acebeam’s P17 Defender.

The 60601-T6 aluminum host is meticulously machined with no defects, gaps, or machine marks anywhere, and the finish is equally nice. It’s still black type III HA, and retains the same durability I’ve enjoyed with Fenix finishes, but the TK21 has the same matte finish as the TK17.

Fenix’s glossy finishes have been a silent gripe of mine over the years, but no more: The TK21R’s new suit gets it out of the prepubescent frat house into the gentleman’s club where Acebeam, Weltool, and ArmyTek reside. It’s more than cosmetic: The new finish also adds grip and just feels more premium.

Only the tail comes off for access to the battery and there’s two springs at work: One for the driver and tail like there should be in a working light, and that makes it weapon-mountable. The rear threads are fully anodized, rectangular cut units that are really smooth and nicely lubed.

The charge port collar has much finer triangular threads with a sealing o-ring at the top. The USB C charge port, per Fenix, is also fully waterproof even when exposed, and Fenix says it’s good for an IP68 rating on ingress and 1.5 meter drop impacts. You can be confident in Fenix’s ratings and they are lab tested.

For the warranty, rest assured because Fenix’s warranty is one of the best, with great customer service to back it up. While service varies depending on where you bought your Fenix, the warranty is the same. From Fenix: 15 days free replacement: Fenix will replace a new product within 15 days of purchase for any manufacturing defects if problems come into being in normal use; We will replace it with the same model. If the model has been discontinued, customers will receive a product with similar or improved model.

5 years free repairs: Fenix will offer free repair within 5 years for lights from the date of purchase if problem develops with normal use. Different warranty period for different products:

• Flashlight, Headlamp, Bike Light and Camping Lantern (without a built-in battery) – 5 years (excludes rechargeable battery)

• Flashlight, Headlamp, Bike Light and Camping Lantern (with a built-in battery) – 2 years (battery included)

• Rechargeable battery, battery charger, bike mount, remote pressure switch – 1 year

Except the products and accessories listed above, other products or free offers provided by Fenix are not covered within the product’s warranty.

Limited Lifetime Warranty: For lights past the free repair warranty period, we provide lifetime repairs but will charge for parts. Fenix Lighting LLC will notify customer the cost of the part before repair. Please note, due to changing technology, not all older lights will be able to be repaired due to parts not being available. In such cases, Fenix Lighting LLC may provide a discount to the customer for the purchase of a newer model.

The free warranty does not cover any damages or failure caused by:

a. Normal wear

b. Rough operation

c. Battery leakage

d. Any defects or damages caused by the improper operations include but not limited to the operation which doesn’t comply with the warranty or notes shown in the product specification. For example, the product specification will describe that please don’t disassemble the sealed head, as doing so can damage to the flashlight and will void the warranty’

e. Any defects or damaged led by other behaviors which can not be controlled by Fenix reasonably.

The TK21R went shopping for a new LED, and conscripted another Luminus product, the SFT-90. Introduced for Q1 2025, this one’s a single homogenous LES, 3 volt, lateral (bond wire) design LED. Usually manufacturers defaulted to the SBT90.2 for the same performance and output targets of the TK21R, but that LED is not only expensive, its large 9090 footprint required more real estate, which limited it to flashlights with larger heads and reflectors.

The SFT-90 LES is the same size as the SBT90.2 at 9.6mm², but has fewer bond wires (16 total versus 24) and a much smaller 7070 (7 mm x 7 mm like the Cree XHP70) footprint. It’s not only much cheaper to produce, but more scalable and easier to fit into a variety of flashlights. While not quite at the same level as the SBT90.2 in terms of output and intensity (owing to the SBT’s lower Vf and higher efficiency), it still achieves 90% of the latter’s output at roughly ¼ the price.

That’s win-win any day. The CCT is cool white (6500K) and low CRI. For the tint, Luminus supposedly tweaked the phosphor on the SFT-90, and improved the tint shift from low to high outputs with a lower +duv.

For the bezel, it’s a very stout matte finish stainless unit with prominent crenulations topped with tungsten glass breaking tips. The bezel extends a way over the hardened AR coated mineral glass lens so it’s protected from smashing windows or drops.

The reflector is a deep SMO unit. Paired with an SMO reflector, the beam has a nice even spill and plenty of side illumination with a very bright, but large center spot. It’s a highly versatile beam with lots of throw for a sub-40 mm head light.

I’d say it throws just as well as a similar-sized reflector with the SBT90.2. In addition, it seems Luminus tweaked their phosphor somewhat as I’m not seeing the very positive duv I’m used to with these CW SFT-xx LEDs and the tint shift isn’t so dramatic.

More details: 

• LED Type: Luminus SFT-90
• High CRI: No
• Focusable beam: No

Spectral measurements: 

I used an Opple Lightmaster Pro to measure the flashlight at 2 meters distance. 

Mode:	CCT:	CRI Ra:	duv
Turbo	6085K	65.1	0.0061
Low	5660K	64.7	0.0082

Dimensions: 

Fenix TK21	Millimeters	Inches
Length	159 mm	6.3 in
Head diameter	36 mm	1.4 in
Body diameter	26 mm	1 in

Dimensions are rounded to the nearest millimeter and the nearest tenth of an Inch.

Weight: 

Weight	Weight in grams	Weight in oz
Without battery:	146 g	5.2 oz
With Fenix ARB-L21-6000 battery	225 g	7.9 oz

Weight is rounded to the nearest gram and tenth of an Oz.

Flashlight size comparison with its competition:

Group 1: Fenix PD35R ACE, Fenix PD36 TAC, Fenix TK16 V2.0, Fenix TK17, Fenix TK20R UE, Fenix TK21R

Group 2: Olight Warrior Ultra, Fenix TK20R UE, Fenix TK21R, Acebeam P17, Klarus XT11GT Pro V2, Olight Warrior X4

Group 3 reflectors: Fenix TK20R UE, Fenix TK21R, Acebeam P17

The TK21R, since it’s not using a 6 volt LED, has a constant current buck driver to pull the 4.2 volts form the battery down to something the LED can use without being damaged. It also carries forward the UI from the TK17, and that’s good and so-so because that UI, which okay for most everything, was still missing instant Turbo. The UI is managed by two switches: The main larger switch called the tactical switch for on-off and access to Burst mode, and the smaller, oval functional switch, which controls mode changes.

Available modes: 

• Low, Med, High, Burst (Turbo)

Available blinky modes:

• Strobe

From OFF Tactical Switch:

• Fully click: Constant on last used mode
• Half-press switch: Momentary on in last used mode
• Press and hold for more than one second: Burst mode

From ON Tactical Switch:

• Fully click: Turns off
• Press and hold: If held for more than one second, Burst mode will activate

From OFF Functional Switch:

• Single click: Strobe

From ON Functional Switch:

• Single click: Changes modes L-M-H-Burst-L
• Press and hold: If held for more than one second, Strobe mode will activate

Mode memory:

• Yes. The brightness levels will be memorized including Burst Mode, which is memorized if activated from ON or OFF in any brightness level. 

Shortcuts:

• To Burst: From OFF press and hold the Tactical switch for more than one second
• To Strobe: Click the Functional switch from OFF for momentary Strobe. From ON pressing and holding the Functional Switch will activate momentary Strobe

Strobe/blinkies

•  Strobe. Momentary only, and activated from ON or OFF with the Functional switch.

Lock-out mode: 

• None, but can mechanically lock the light by unscrewing the tailcap

PWM

• None visible by the naked eye

Additional/summary info on the UI: 

• The changes to the UI, while welcome for better versatility and simplicity (really, the Eco mode wasn’t needed), still didn’t address the main issue of Fenix’s tactical-use oriented flashlight UIs: Lack of instant-on max brightness. In my opinion, this is a must-have if doing any tactical work, just as important as instant Strobe (which this has). As-is though, the UI is fine for general purpose and duty work, and could be learned easily quickly by anyone. 
• I’m happy with the brightness levels (they make sense), and there’s also intelligent temperature management and LVP with a visual notifier.

The TK21R carries forward the 21700 size cell for power. Fenix bundled their 6 Ah ARB-L21-6000 with the light. The ‘R’ here designates onboard charging, and I’m happy to report that Fenix upgraded the charging for the 21R 

Also, mad props to Fenix for being one of the holdouts in this segment since they let you bring your own batteries to the TK party. I tried a bunch of other cells and they fit just fine: Acebeam’s ARC and INR series 21700s with USB (which are very long) and without worked, flat top unprotected cells were too short, but button top protected and unprotected fit fine. Note that if using a non ARB-L battery, the LVP functions don’t work (the LED and blinking notifier).

The onboard charging layout is identical to the TK20R V2, with a collar that unscrews to expose the USB C port and indicator LED. I like the port cover design (but not the hidden indicator LED), since it’s going to be very well protected and easier to access than a rubber plug. I don’t like how the indicator LED is under the cover, so you can’t see it without opening it.

The charging speed has also been tweaked from 5V 2A to QC-level 5V 3A or 9V 2A. Nice. This addresses another quiet gripe of mine with Fenix handhelds: Slow charging, but now the TK21R should charge the 6 Ah cell in 2 hours 6 minutes. For LVP, besides the battery indicator, the TK21R will flash the main LED to indicate low voltage. During operation, when the battery drops to under 25%, the output will drop dramatically and the main LED will blink three times every 5 minutes.

Battery level indicator:

• Solid green light: 85% to 100%
• Flashing green light: 50% to 85%
• Solid red light: 25% to 50%
• Flashing red light: 1% to 25%

Batteries	Details
Compatible batteries	1*21700
Incompatible batteries	None I had
Low voltage protection/warning	Blink
Onboard Charging:
Onboard charging	Yes
Power bank functionality	No
USB-C to USB-C charging	Yes
Max power of USB charger (port)	45 watts
Max power measured	20 watts / 9 V 2.18 A
Final battery voltage (charged)	4.18 V
Avg. onboard charge time	2h 6 min

Lumen measurements

How Lumens are Measured: Understanding ANSI FL1 Standards How Lumens are Measured: Understanding ANSI FL1 Standards: The ANSI FL1 standards specify that output in lumens should be measured 30 seconds after turning on, as this is the standardized time for measuring brightness according to the industry standard. This is why we focus on this part in our measurements. The ANSI FL1 standards require an ambient temperature of 22 ± 3°C. We record the ambient the ambient temperature to identify potential reasons for any observed discrepancies.

Lumens are measured in my 50 cm integrating sphere with a Digi-Sense 20250-00 data logging luxmeter. The sphere has been calibrated with a Convoy S2+ measured to 260 Lumens and the figures are within 10% of actual. I tried to get current outputs, but the weird design of the current path (no signal tube) made that impossible. Outputs measured using a fully charged Fenix ARB-L21-6000 6Ah 21700.

Mode	Amps at start	Specified output	Turn on	30 sec.	10 min.
Low	N/A	30 lm	31 lm	31 lm	–
Medium	N/A	350 lm	343 lm	343 lm	336 lm
High	N/A	1,000 lm	1,029 lm	1,022 lm	985 lm
Burst	N/A	3,600 lm	3,723 lm	3,212 lm	949 lm

*Turn-on and 30 second measurements are done manually, while the 10-minutes readings comes from the runtime graph. This is our standard approach, though some reviewers may choose a different approach.

Ambient temperature during testing:

• 21 °C 

Parasitic drain: N/A

The outputs look great. Burst is coming in hot for turn-on, but settles down by ANSI. The SFT-90, while I couldn’t get current figures, is probably drawing more current than the TK17’s XHP50.3 LED owing to the lower vF (it heats up faster too).

Battery Life: Runtime graphs

How Runtimes are Measured: Understanding ANSI FL1 Standards About ANSI FL1 runtime standards: The runtime is measured until the light drops to 10% of its initial output (30 seconds after turning on). This does not mean that the flashlight is not usable anymore. The last column shows how long the light actually works till it shuts off. If there is a + symbol, it means that the test was stopped at that particular point, but the light was actually still running. This happens on certain occasions, with certain drivers, firmware, or batteries.

Lumens are measured in my 50 cm integrating sphere with a Digi-Sense 20250-00 data logging luxmeter. The sphere has been calibrated with a Convoy S2+ measured to 260 Lumens and the figures are within 10% of actual. I use a Digi-Sense 20250-92 data logging thermocouple for the temperature measurements. The probe is affixed to the head using kapton tape and uses the same 5 second sampling rate for logging. Runtimes were conducted using the fully charged Fenix ARB-L21-6000 6Ah 21700.

Mode	Specified runtime	Runtime (ANSI FL1)	Time till shut off*
Medium	7h 30min	8h 6min	8h 7min
High	3h 30min	3h 34min	5h 4min
Burst	2h 30min	2h 31min	2h 38min+

*The last column reflects the total runtime until the light turns off. A “+” symbol indicates that the test was stopped at that point, but the light continued to run. This typically occurs with certain drivers, firmware, or battery types.

For the runtimes, we see my testing agreeing with the advertised specs. I actually ran Burst mode twice. The first run the output wasn’t very laminar, and seemed like the output may have been throttling a bit.

I re-ran the Burst test later in the day when it cooled down a bit, and that didn’t help much. The output didn’t track straight and uninterrupted. This is very uncharacteristic for Fenix because I’m used to seeing arrow-straight plots on my graphs from their higher-end lights. 

Either way, Burst and High at turn-on are over spec. Burst drops to 3,212 Lumens by ANSI and drops steadily until a step-down by 120 seconds down to around 1,000 Lumens. Still, you get 2,000 Lumens or more for almost 2 minutes, which is good for a small light, and the output oscillates between 870 and 1,022 Lumens over the next hour 45 minutes before smoothing out at 800 Lumens for the remainder of the regulated output.

LVP hits and pulls the output down for Burst and High, with the main LED flashing away every 5 minutes. I ended the Burst test, but High and Medium shut down on their own. The regulated output for Bust and High are close and nearly track together at around 950 Lumens, which is pretty good and what I expect from a leader brand 21700 light these days.

The battery was discharged to 2.8 to 2.9 volts and the thermal regulation looks good on Burst mode, with some oscillation as the output throttled. This was also replicated in the re-test, so the 3 volt SFT-90 LED must be creating more heat than the TK20R V2 or TK17 (which have boost drivers). Still temps never went over 60 C, and the light was hand-friendly the entirety of the testing.

For the comparison graphs, the TK21R is up against the best of the best in duty and tactical lights and holds its own, running close to the Olight Warrior X4 and Sofirn SK40 (which costs $45). Fenix’s newest TK17 and slightly-older TK20R UE lag behind.

Peak beam intensity and beam distance measurements

About Peak beam intensity: Understanding ANSI FL1 Standards About peak beam intensity The calculated value of distance in meters at which the flashlight produces a light intensity of 0.25 lux. (0.25 lux is about the brightness of a full moon shining on an object). This means that the intensity has decreased so much, it becomes difficult to see darker objects, or objects that don’t reflect light. The columns ‘Meters’ and ‘Yards’ use rounded numbers.

Beam distances are measured using a Uni-T UT383S luxmeter measured indoors at 5 meters.. Measurements taken at 30 seconds using the fully charged Fenix ARB-L21-6000 6Ah 21700. The light was allowed to cool and recharge between the High and Burst tests.

Mode	Specified intensity	Specified beam distance	Candela measured	Meters	Yards
Low	500 cd	45 m	500 cd	45 m	49 yd
Medium	5,860 cd	150 m	6,300 cd	159 m	174 yd
High	17,000 cd	260 m	17,952 cd	268 m	293 yd
Burst	58,000 cd	480 m	57,025 cd	477 m	522 yd

Ambient temperature during testing:

• 21°C 

Throw figures are on the money here, like I expect, and the new SFT-90 really wakes up the TK2x series in a big way. At turn-on, Burst came in at 63,800 cd for 505 meters. Impressive considering the sub-40 mm head and high output.

Camera settings and distance: Photos taken with a Canon EOS R100 with Canon RF-S 18-45 mm STM lens. The fence is 95 meters away. The camera is set to 0.3s, F5 ISO1600 and 5000K WB. 

Beamshots of the following flashlights compared:

• Fenix TK21R
• Fenix TK17
• Fenix TK16 V2.0
• Fenix TK20R V2
• Acebeam P18
• Klarus XT11GT V2 Pro

Please note that the following beamshots are mainly intended to showcase the beam pattern and beam quality, rather than overall performance. These images are typically taken directly after activation, and in different seasons or weather conditions, and therefore do not fully represent its overall performance. In few cases the camera settings are even different and therefore not meant for performance comparisons. For accurate performance metrics, such as output, beam distance, and runtimes, you need to look at the performance section of this review.

Disclaimer: This flashlight was sent to us for review at no cost by Fenix Lighting. We have not been paid to review, nor have we been holding back on problems or defects.

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