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Reviews Appreciation

Fenix TK 51 Review

Publish Time:2013-12-12

First Impressions

Whenever I unboxed this light I was a bit surprised at the overall size.  The grip seems to be a similar large barrel, close to the size of the TK 75 also produced by Fenix.  The overall feel of the flashlight is on par with the build of every Fenix product I’ve owned or tried - high grade aircraft aluminum in a sleek design.  Given the larger size of this light it is well balanced and doesn’t feel awkward to carry when in use.  For storing, this is definitely something to tuck away in the pack - 430 grams without the battery cell and likely an additional 350 grams in weight when installed.  Fenix recommends unscrewing the rear cap ½ turn to prevent the light from accidentally turning on while in transport. A quick opening of the rear battery cap reveals a white cell housing three of Fenix’s ARB-L2 rechargeable lithium ion batteries (aka 18650) with a built in protection circuit.  

A size comparison between the TK 51 and my Garmin 62s handheld GPS unit.

My general thoughts are that light would make a great tool for a search and rescue group or if your application of use can justify the larger size and weight.  I couldn’t see many people justifying carrying this on a regular basis, especially those conscience of space and weight in their packs.  My personal interest in this light is its ability to use one or both beams to light paint for long exposure photography and backcountry travel.  So, with all this in mind I’ll look at what this light can do for me as a photographer and some of the pros and cons of general usage.  

To start with, I’ll showcase the specs of the TK 51 as presented by Fenix.

General Specifications


The TK 51 is a dual beam flashlight utilizing two Cree XM-L 2 LED bulbs rated at 50,000 hours of use.  Each LED button four output setting LED’s that produce a total of 900 lumen beams,

one spot and one flood, to deliver a total of 1800 lumen output.  These are super bright, incredible little bulbs that pack a huge punch.  Careful not to look into the light!

A showcase of the main LED (spot beam) and the side bubble that houses the flood beam on the TK 51.


The TK 51 uses a battery core that holds 3 -18650 rechargeable lithium ion batteries (Fenix model ARB-L2).  If needed, the flashlight can use 6 -CR123A’s but with the tradeoff with decreased lumen output and battery life.  I am typically a big fan of AA battery flashlights since I travel, but with a charging unit this seems like a potentially solid option to carry.  Pair this up with a solar charging system and you are golden.

The TK 51 with the battery ‘core’ removed

Overall Operations

The TK 51 has a ‘control center’ that utilizes three main buttons to control all functions.  The main ‘off/on’ button, also referred to as ‘general mode.’ controls the basic power function of  on and off for both the spot and flood LED’s.  This button is also used to power back on the light in the previous modes of the spot and flood functions as part of the intelligent memory system.   I’ll touch on this control system later on .

LED specific controls

The Floodlight and Spotlight both have four specific settings for the LEDs - Low, Mid, High, Turbo, and a fifth powers the bulb off.  This allows for specific fine tuning of light output for the situational need.  

Instant Turbo Modes and Strobe activation

The TK 51 offers quick access turbo mode function - depressing the general power button for 1 second will activate the maximum output mode for both spot and flood LED’s.  Depressing the specific flood or spot LED buttons for 1 second will activate the strobe functions of the TK 51 (specific to the button depressed).  

Output Lockout & Overheating Protection

The intelligent features of the TK 51 offers the ability to sense when the batteries can no longer sustain current brightness levels and drops the output level of the flashlight.  This function is unlocked when batteries are recharged or replaced.  

If the flashlight experiences potential overheating (in turbo mode), the TK 51 is programmed to downshift to the high brightness level.

In the field

To test out this torch I headed out on multiple late evening hikes to Moscow Mountain in western Idaho.  The Palouse region of eastern Washington and western Idaho suffer from very little light pollution and with no moon early on the test nights, conditions were great what I wanted to demonstrate with the TK 51.  In addition to taking it in the field, I utilized the light frequently around home to see if there was any noticeable drop in battery life over the test period.

The weight for me is lost in the sea of camera equipment and accessories when I’m out on the trail, so this little addition impact me other than finding somewhere to stash it to prevent damage to the lens.  I would suggest a case/pouch for this to prevent damage up front.  

The big output of 1800 lumens from two LEDs is quite the substantial light output from what I’m typically used to.  I’ve used my smaller Fenix LD22 (220 lumens) in camp, on the trail and as a tool in long exposure photography with some success.  The TK 51’s variable beam options from the dual LEDs allows you to toggle through settings to accommodate your situation with the right amount of light.  

Showcasing the individual beam performance of the spot LED from low to high

A demonstration of the flood beam output from low to high

This light performed admirably in low light and dark situations in which I swept through trail areas and off the trail, simulating normal use for a night hike or potentially what a SAR member would be doing with the light.  Even after a few hours of being out with the TK 51 it never felt cumbersome.  However, as the temps got colder and I threw on my heavier gloves, operating the light became a bit more difficult - the buttons for both LEDs are small and near impossible to toggle through.  Obviously this is a seasonal nit, but I prefer the single raised rubber on/off switch of the smaller Fenix models and the side mounted output selector.  I cycled through the various LED modes for photo ops as well as long exposure work and some light painting, targeting the type of uses I’d employ this light if carrying it on a photography trip or out into the backcountry.

Using the TK 51 in all of its 1800 lumen glory to light the woods of Moscow Mountain, Idaho.

During the course of the test period I made myself use the light both in the field and at home testing some of the basic features of the light such as battery life and the waterproof rating.  Over the course of 2 weeks the power output shows no noticeable drop on output.  The rechargeable battery systems seems to hold a great deal of charge and it will be worth noting how the Fenix batteries last over the long term.  To test out the waterproofing I decided to go a different route than the typical ‘dunking’ in the creek.  I buried the TK 51 in about 6” of snow for about a half hour.  After that time, I pulled the TK 51 back out of the snowpack (which had been melting around the light, soaking it) and fired it up with no problems!

Overall Thoughts

This is a remarkable tool to use in outdoor recreation, search and rescue, photography or to utilize as an emergency light for home or vehicle.  Even with multiple modes and settings its rather simple to use and carries the high quality of the Fenix brand.  Being a fan of the Fenix lights that support standard AA batteries, the rechargeable battery system is efficient and I’m excited to see what kind of longevity I can obtain out of the Fenix lithium ion batteries.  What may deter some is the overall size and weight of this light compared to some of the smaller, powerful lights in the PD and TK series.  Also, depending on the application, 1800 lumens could be a bit overkill for use in camp or the outdoors where smaller, 400-600 lumen models would perform just as well.

Hitting the trail on the descent from the Headwaters Loop of Moscow Mountain.

My biggest qualm with the unit is the button interface as compared to other models from Fenix.  The buttons are smaller and more flush to the grip than what I am typically use to, so trying to figure out settings in the dark or through gloves becomes a bit of a challenge.  Overall, this is still a great high powered torch that can get the job done.  I would recommend this to any outdoor enthusiast or photographer that needs a high power unit for their use and isn’t wanting to drop the additional money/have a need for the output of the TK 75.

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