Fenix TK21 (XM-L U2 | 1 x 18650)

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Fenix TK21 (XM-L U2 | 1 x 18650)

It's been a while since I've had a new Fenix. Back in early 2008 when I first got into this hobby, a L0D was actually the second light I added to my then budding collection. That was followed by a LD10 in early 2009 but I gave that away shortly after acquistion to one of my in-law's. As the years went on since the LD10, for whatever reason I just didn't acquire another Fenix light even though I've had great experiences with the two. The L0D was actually my EDC for a while but had fallen out of favor as I prefer 1 x 123 format. My "New Fenix-less" status changed back in June as I was one of the lucky winners of a give-away for a Fenix TK21 U2 on CPFMP.

Let's see what Fenix has to offer in one of their latest releases.

• Cree XM-L (U2) LED with a lifespan of 50,000 hours
• Uses two 3V CR123A batteries (Lithium) or one 18650 rechargeable battery (Li-ion)
• 150mm (Length) x 25.4mm (Diameter) x 40mm (Head)
• 152.6-gram weight (excluding batteries)
• Digitally regulated output - maintains constant brightness
• Reverse polarity protection, to protect from improper battery installation
• Push button switch with momentary-on function
• Made of durable aircraft-grade aluminum
• Premium Type III hard-anodized anti-abrasive finish
• Toughened ultra-clear glass lens with anti-reflective coating


The packaging is standard fare for lights in its class with an outer cardboard box with a display window showcasing the light and then there is a plastic inner shell that holds the light, accessories and manual. There is no indication on the box that this is the Special Edition U2 version, however, the manual does state it's an U2:

Supplied with the light were:
- User Manual
- Warranty sheet
- Holster
- 2 x Powerizer CR123
- Accessories bag containing:
* 1 x spare rubber tailcap cover
* 1 x spare o-ring
* 1 x wrist strap (it's a stretch to call this a lanyard)


The TK21 features Cree's XM-L LED and the U2 designation means that it's using the highest luminous bin vs. the more common (for now) T6. The claimed output is also up slightly from 449 lumens for the T6 to 468 lumens for the U2.

EDIT: 8/27 Apparently, this was the only version ever released as Fenix was able to secure sufficient amounts of U2 bin and thus never released a T6 version.

The mini-turbo head is a single integrated unit that does not feature a removable bezel. I've noticed that it seems to be increasingly common with recently released lights that the head is glued and not-removable as well. While the manual states that the glass features anti-reflective coating, I wasn't able to see this on the outside (usually indicated by the tell-tale blue reflection):

Perhaps it was only applied on the inside.

The tip of the head is also completely flat so it'll sit flush against a flat surface when stood on it's head thus you won't be able to tell if the light is on or not (I tipped the light slightly in the last shot to show that it was indeed on):

The engravings are very fine and sharp with no noticeable defects. What i found interesting though is that the HOT symbol was engraved over different angles without any flaws whatsoever:

I'm not familiar with the process so perhaps someone more knowledgeable can pipe in on how it's done.

While we're on the topic of the HOT symbol; the light for the most part respects design symmetries (e.g. the Logo and Model are centered with the button, the cut angles and different facets are symmetrical on both sides). Where this deviates is, you guessed it, the HOT symbol (and the serial number). They are not centered with the button or logo/model. Neither is the groove on the head:

Ultimately not a big deal and symmetrophobes would feel right at home with this aspect.

Around the "throat" of the light, we find a silver button that controls level changes (more on this later). The button sits on a flat surface that is also featured on the opposite side (again respect to symmetry comes in to play here).

This was actually a very thoughtful design as the tip of the index finger rests on this flat surface (right pic) providing stability when depressing the button.

There is a tactical-ring that can aid with anti-roll which can be removed revealing non-squared threads:

However this didn't detract from the smoothness when screwing it on.

The rubber boot on the tailcap extends past the end of the prongs on the tail and as such, renders it non-tailstandable:

The light features springs in both the head and tail ends which should help absorb shock and even when I shook it very hard, I was not able to induce any battery rattle:

Removing the tailcap exposes nice squared threads:

As can be seen above, a AW2600 just peaks out of the tube so longer batteries might pose a problem so you may wish to check this before committing to a purchase if you have really long batteries

While the holster accomodates the light snugly, I feel it was either more of an afterthought or a generic one that was repurposed for this light as the flap seems just a little short and thus exposes the Velcro to the head of the light which in the long run, may potentially scratch up the finish:

As for the strap (bottom one in the pic), after playing it around with it a bit, I'm sure it's more than up to the task of securing the light in case it slips however, it just doesn't inspire the same confidence that a true lanyard (not included, this was only for illustration purposes) gives:

Owing to the mini-turbohead (1.53" in diameter), the light is towards the larger end of the 1x18650, 2x123 sized lights:

From L to R: Fenix TK21 | SF U2 | Olight M20 | SF E2DL | SF Z2 | SF G2Z | SF L4 | SWM T20C

I can definitely feel a bias in weight towards the head but nothing overbearing so as to make it very unbalanced.

Fit and finish is as I recall my earlier Fenix's to be which is pretty good. The HA finish is flawless and matched perfectly between all parts:

(flash was intentionally used to try to expose mismatches in the anodizing but as you can see, there is none to be found)

The textured finish on the tube is a bit smooth and doesn't really offer much in the way of additional grip, however the texture on the tailcap is a bit better and improves grip when changing batteries:

However, looking down the battery tube, I noticed some residual burr from what looks to be the mating between the battery tube and the the throat of the light:

It hasn't scratched my batteries so far but I am concerned about that fragment in the long term so will look to get that removed shortly.

The light has a main foward clicky switch that serves only to turn the light on/off in momentary or "latched". All mode changes are done via the silver button on the throat of the light. This button is used only to change levels and to access the hidden strobe, it will not turn the light on/off. Depressing the button will cycle the light through L, M, H, T successively and always in that order. So let's say you are in M, upon depressing the silver button once, it will cycle to H and so on and so forth

The light has a really neat feature in that it will actually fade up or down to the next level. It's cool to see it dim quickly from Turbo to Low mode rather than the abrupt level changes I've grown accustomed to with all other lights that do not feature variable control.

Strobe is hidden and is both actived and deactivated by holding the silver button for at least two seconds. It will always come on in full blast T mode. When activating strobe, it will first cycle to the next mode but upon deactivation, it will revert back to your original mode. So let's say you were in M and you wish to activate Strobe, it will first cycle to H immediately upon the button being pressed and then will go into Strobe mode. Upon deactivating the strobe it will revert back to the original mode you were in before you activated the strobe. I tested this in all 4 modes to confirm the behavior is consistent.

The only time I kind of see this being a problem is if you were in T and for whatever reason you needed the full blast Strobe, that temporary reduction to L may not be desired and inconsistent with your need to activate strobe in the first place (unless of course it's just for show & tell).

Edit 8/27: Mfg Claims (ANSI):

I used various rechargeable battery combo's to provide an idea of what you can expect with similar batteries that you might own. The relevant battery stats are provided above each runtime graph along with:
- Voltage of the battery at the start and end of the test
- Current draw as taken right before the test (only AW2600 so far)
- Actual runtime until the battery cut out (first in HR and then in M so read this as 1.3 Hrs OR 79 Min)
- For testing on Turbo only (in which case a fan was used), temperature: ambient, the head at start and the max it reached

Axis: X = Time in Min and Y = Relative Output

My unit didn't live up to the mfg's claim (1h 50m) on Turbo. At best, I was only able to squeeze out 79m before it kicked down to High mode.

EDIT 9/26: In re-reading the ANSI standards, which to recap is the total runtime until light reaches 10% output from original value measured 30 seconds after light was turned on, I not only matched but exceeded ANSI claims for Turbo since the light stayed on High through about 175min on AW2600 which is just shy of 3hrs. I've added a 2nd battery/runtime stats to show the ANSI runtimes achieved.

I've also revised the runtime on Turbo since I just got in some brand new RediLast batteries rated @ 3100mAh. While it didn't help the light stay in Turbo any longer than the AW, it did extend the total runtime on H by nearly .5hr until it dropped out.

On high I was able to exceeded mfg's claim using AW 2600's: 6.2hrs vs. 5.17hrs.

Edit 8/29
Current draw on Med and L were measured as 111mA & 13.4mA respectively on an AW2600 so on paper, this should yield 23.42H & 194H respectively.

Of the XM-L lights that I own (T20C, Manafont Drop-In, TK21), this is definitely the greenest tint. The hue is most evident in the corona surrounding the hotspot while whitewall hunting, however, it's also quite prominent here in this day time pic in direct sunlight for comparo:

All shots on Canon S3 IS using WB that yields the closest to what my eyes see (left = 1/13" @ f2.7 | right = 1/80" @ f2.7)



OLT M20 w/Manafont XM-L 3S Drop-In SM

DBS V2 w/Manafont XM-L 3S Drop-In SM


LMP VX Ultra w/XR-E R2 & TurboForce Kit


SF G2Z w/Neofab D1000

SF Z2 w/Malkoff M60






SF E1E w/kuku427 Warm XP-G 3S Tower

For other indoor shots and comparison vs. many other lights, please see here.

Here are some quick outdoor shots. For full details and comparo vs. 23 other lights, please see here.


I recently completed some long distance outdoors shots. For full details and comparo vs. other lights, see here.


Disclosure: The TK21 was won via a promotion.

Edited by: turboBB on 02/14/2012 - 00:37
harry25175's picture
Last seen: 7 years 10 months ago
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damn... you have so many nice light.....

BIGWOOD's picture
Last seen: 6 months 3 weeks ago
Joined: 11/17/2011 - 16:16
Posts: 702
Location: Vancouver, BC

That's a nice quality light.  Cop next door uses one on his duty belt and let me play with it.  If only he let me take is S&W and shoot off a few rounds or take his swad car and do couple donuts in the parking lot with the sirens on that would be even better.  I doubt it.

This is one of the lights I have short-listed to go on my (soon to be acquired) rifle.

Thanks for the review.  Nice pics too.

Last seen: 9 months 3 weeks ago
Joined: 09/10/2011 - 00:32
Posts: 803
Location: NJ, US

Thx!  Just one thing is to watch out for that little metal notch in the tube.  On another forum one member has mentioned it's not a big deal, I personally think it is.  It has already scratched up the wrap on one of my batteries and if using a protected one and the strip for the PCB protection so happens to be aligned with it, it might cut that as well (especially considering that you'll be mounting this on a rifle).

Best to speak to the prospective dealer if they can check this in advance for you as I'm not sure if every single TK21 has it or not.


Last seen: 6 years 10 months ago
Joined: 10/12/2011 - 15:18
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Location: Italy

Ty Tim, you ever do great reviews and have so much cool flashlight I'm envy xD

Last seen: 9 months 3 weeks ago
Joined: 09/10/2011 - 00:32
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Location: NJ, US

Thx!  The madnes... er, hobby started 4 years ago w/a Dereelight DBS and has evolved into what it is today. =o)

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Nice review, Tim!  I never tire of looking at your photos.  Your macros are out of this world!!  Keep up the great job. Cool


Chicago X
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Some of those pics would be right at-home in the company's catalog.

Very well-done.


War Dogs, Making it Home - Rescue Dogs for Returning Vets

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That's a nice light and a good job! 

jacktheclipper's picture
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Excellent .

What I do


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Nice pictures!

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Excellent review. You put a tremendious amount of detail and work into these. I really enjoy reading them. Well done!



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Don wrote:

"But as I said long ago, you are more likely to be killed by a dead fish dropped by a seagull in the Sahara Desert than by a lithium ion

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Apart from being a flashoholic you are an excellent photographer (and have a lot of money Cool).


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Nice review!

Prisoner 6-2-7

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Wonderful review I just received one of these saturday.