Warning: pic heavy, as usual.
The TK51 from Fenix features an unusual build – a 3x18650-class flashlight with separate XM-L2 emitters to emphasize either throw ("spot") or spill ("flood"). More interesting still, you can control both emitters independently, giving you a wide range of possible combinations.
Note that this review – which was part of Fenix's "global testing campaign" - was delayed while Fenix worked to resolve an issue I had discovered with the battery carrier on my sample. More on that early issue in post #2, after the full review.
Let's see what the official specs have to say ...
Manufacturer Reported Specifications:
(note: as always, these are simply what the manufacturer provides – scroll down to see my actual testing results).
- Utilizes two Cree XM-L2 (U2) LEDs
- Single Light Specs: Turbo - 900 Lumens - 3 hr, High - 400 Lumens - 9 hr, Mid - 150 Lumens - 27 hr, Low - 10 Lumens - 429 hr.
- Two Lights Specs: Turbo - 1800 Lumens - 1 hr. 45 min, High - 800 Lumens - 4 hr. 30 min, Mid - 300 Lumens - 13 hrs. 30 min, Low - 20 Lumens - 210 hrs, Strobe - 1800 Lumens.
- SPOT LIGHT: 900-Lumen max output with 425-meter beam distance throw (45,200cd beam intensity) for long-rang lighting
- FLOOD LIGHT: 900-Lumen max output for close-range coverage
- Digitally regulated output with low-voltage indicator
- Reverse polarity protection guards against improper battery installation
- Three-button interface for fast and convenient operation
- Made of durable aircraft-grade aluminum
- Premium Type III hard-anodized anti-abrasive finish
- Toughened ultra-clear glass lens with anti-reflective coating
- Individually controlled spot & flood
- 16 flood and spot combinations
- Three-button interface for last and convenient operation
- Instant turbo to allow immediate output even when the light is off
- Instant strobe to access immediate access to the strobe even when the light is off
- IPX-8 Standard. Waterproof to 2 meters for 30 minutes
- Size: 430-gram weight (excluding the battery), 188 mm Length x 48 mm Diameter
- Batteries Used (Not Included): Can be powered by one, two, or three 18650 batteries or six, four, or two CR123A Non-rechargeable batteries
- Prolong use of operating the light with one or two 18650 batteries will shorten the life span of the rechargeable battery.
- When powered by CR123A batteries, the runtime of each brightness level will be shortened
- MSRP: ~$160
I don't know what final packaging will look like, but I suspect it will be similar to other recent Fenix lights.
From left to right: Eagletac Protected 18650 3400mAh; Fenix TK51, TK45, TK75; L3 Illumination (SupBeam) X40; Eagletac SX25L3.
All dimensions directly measured, and given with no batteries installed:
Fenix TK51: Weight: 476.9g (627g with 3x18650), Length: 187mm, Width (bezel narrowest): 58.2mm, (bezel widest): 70.8mm
Fenix TK45: Weight: 307.3g (514.7g with 8xAA), Length: 202mm, Width (bezel base) 50.6mm, Width (tailcap) 44.0
Fenix TK75: Weight: 516.0g (700g with 4x18650), Length: 184mm, Width (bezel): 87.5mm
Eagletac SX25L3 3x18650: Weight: 315.9g, Length: 150.2mm, Weight (bezel): 47.0mm
L3 Illumination X40: Weight: 517.2g (655g with 4x18650), Length: 182mm, Width (bezel): 68.0mm
Nitecore TM15: Weight: 450.6g (634g with 4x18650). Length: 158mm, Width (bezel): 59.5mm
Niwalker BK-FA01 (shipping): Weight: 687.6g (870g with 4x18650), Length: 209mm, Width (bezel): 80.0mm, Width (tailcap): 50.3mm
Thrunite TN30: Weight: 468.2g (est 620g with 3x18650), Length: 179mm, Width (bezel): 64.3mm, Width (tailcap): 49.0mm
The most distinctive aspect of the TK51 is the head, but I'll save that until the end. As usual for a high-end Fenix light, the TK51 has a substantial and solid build. Anodizing is a flat black, and seems in very good shape on my sample. Body labels are fairly limited on my review sample, but crisp and clear.
As with other recent Fenix lights in this TK-series class, there is no knurling per se on the light. Rather, there is an overall checkered pattern on the handle. Each checkered segment has a large number of tiny concentric ring ridges. This contributes to fairly decent grip. Combined with the other build elements and ridge detail, you should find overall grip good.
Threads are square-cut, and generally seem of good quality. Threads are anodized, but you have to turn the head at least a half full turn to reliably lock out the light (due the tension on the contact springs maintaining contact with the battery carrier).
Like other recent Fenix TK-series lights, there are a couple of electronic switches in the head to control on/off and mode switching. The top left switch controls on/off and mode switching for the "flood" emitter, the right switch controls on/off and mode switching for the "throw" emitter. The bottom switch turns on/off both emitters, at their last memorized level. Switch feel is good, and there is a definite "click" when making full contact. Scroll down to my User Interface section for more info.
Inside the head, there are three spring-mounted contact points for the carrier (the outside two for the negative current path, the inside one for the positive current path).
Let's look at the battery carrier:
The carrier is made of solid plastic, very reminiscent to the TK75. The plastic is quite thick, with a sturdy feel. The bays appear wide enough to accommodate a wide range of cell diameters, although I found them tight for length with longer cells. The raised contact disc at the positive terminal means flat-top cells will work fine.
As with the TK75, there are a few nice touches – like the slight cut-outs near the positive terminals, to facilitate getting your cells out. Note that the carrier still connects the same way as earlier models, through the inner and outer spring contacts on the head of the carrier.
One thing that is interesting is that there is a circuit inside the carrier that draws a small current as soon as a cell is inserted. See my current measures later in this review. I will discuss this further in post #2 as well.
The carrier is in 1s3p arrangement (i.e., all wells in parallel). This means that you could easily run 1x or 2x 18650 cells in a pinch. Of course, I strongly advise against trying to run the light on Turbo on both emitters this way, as you would exceed the discharge rate capabilities of the cells (although I suppose IMR 18650 may be able to handle it). A single emitter should be able to handle 1x or 2x18650 just fine, though.
CR123A can also be run in the light, in 2x, 4x or 6xCR123A configuration (i.e., the circuit can apparently handle the higher voltage source of 2xCR123A per well). Note that 2xCR123A can run hotter than 1x18650, due to the differing chemistries, so you should keep that in mind and limit time on Turbo on both emitters with these cells. And again, you should always limit output if you are not using the full complement of 6xCR123A. It's nice to see the CR123A support here, as this was missing on some of the other TK-series lights.
And as always, I urge you to take care and make sure you insert the cells correctly in the carrier (i.e., partially inverted cells would lead to rapid reverse-charging damage to the cells and carrier).
Let's take a look at the truly innovative part of this light, the head:
This is an interesting way to provide both throw and flood simultaneously – two emitters, with distinct reflectors, and independent controls. As you can see, both reflectors are quite smooth, and fully separate from each other. The throw reflector is fairly deep, and the flood reflector is very small and shallow. Emitters were well centered on my sample.
Similar to the other members of the Fenix TK-series, the TK51 uses a series of electronic switches to control on/off and mode selection. These are located just under head, in the traditional location of mainstream consumer flashlights.
The difference with the TK51 is the upper two buttons control the two emitters independently, and the bottom controls both emitters simultaneously. You also don't have separate controls for On/Off and mode changing (like on some other TK-series lights).
To turn just the flood emitter On or Off, click (press-release) the left upper power button. The flood emitter will come on in Lo. Click the switch again to advance in sequence through all the output modes: Lo > Med > Hi > Turbo > Off. There is no mode memory for the independent controls.
For the throw emitter, click the upper right power button. The switch works exactly the same way as described above for the left flood button. Note the two buttons are independent, so you can set either emitter to whatever level you like.
The bottom power button turns on/off both emitters simultaneously, at whatever level they were last set to. So, for example, if you set the Flood emitter to Lo and the Throw emitter to Hi, and then turned Off the light by the bottom button - when next you re-activate by the bottom button, you will be in Lo/Hi for these emitters.
If you press-and-hold the lower power button for more than 1 sec, the light jumps to On in full power Turbo on both emitters, in momentary mode (i.e., release to turn off the light). This works whether the emitters are already on or off. It has no effect on level memory, which returns to previous set for each emitter after you release the switch.
To activate the Strobe mode, press and hold one of the individual upper emitter power buttons for more than one second. Again, you can control the output level of the two emitters separately (i.e., turn both On just one or both in strobe).
For information on the light, including the build and user interface, please see my video overview:
Video was recorded in 720p, but YouTube typically defaults to 360p. Once the video is running, you can click on the configuration settings icon and select the higher 480p to 720p options. You can also run full-screen.
As with all my videos, I recommend you have annotations turned on. I commonly update the commentary with additional information or clarifications before publicly releasing the video.
As with most Fenix lights, there is no PWM, on any level. I did not detect any circuit noise on my sample either.
Strobe modes are exactly the same for the two emitters, with an alternating 2 secs of 6.7Hz and 15.7 Hz strobe. Here is a close up of the slow and fast portions of this strobe:
15.7Hz Strobe portion:
6.7Hz Strobe portion:
Due to the electronic switch, the TK51 has to have a constant parasitic stand-by current drain when the head is connected to the carrier. I have measured this standby current at 33.3uA. Given the 1s3p arrangement (and the high capacity of 18650 cells), that should yield a completely nominal drain – however, it isn't quite that simple.
What you wouldn't expect is that the carrier has a circuit with its own internal current drain. I have measured the three wells of my replacement TK51 carrier one at a time, and each has exactly the same drain: 75.4uA. To find out why I decided to do this, please scroll down to post #2. Long story short, each battery is exposed to an identical drain when in the carrier, regardless of how many other wells are occupied.
To get the appropriate cumulative drain measure, you therefore have to add up all the individual drains for each battery in the carrier, and then add the additional drain from the circuit in the head (keeping track of the appropriate serial/parallel relationships). For 3100mAh cells, that would mean a little over 4 years before each cell would be fully drained.
This is quite reasonable. But note that the bulk of the drain cannot be broken by simply unscrewing the head (although this will break the risk of accidental activation). If you are concerned about the drain, you actually have to pull all three cells from the carrier.
For white-wall beamshots below, all lights are on Max output on an AW protected 18650 batteries. Lights are about ~0.75 meter from a white wall (with the camera ~1.25 meters back from the wall). Automatic white balance on the camera, to minimize tint differences.
Keep in mind that the distance above is ridiculously close to the wall – at proper distances, the two emitters complement each other quite well (i.e., not offset , as you see here).
Here's a comparison of the throw emitter to single 1x18650, 1xXM-L2 lights:
As you can see, the TK51 on its throw emitter has more throw than a typical good 1x18650 light – plus a wider spillbeam.
I don't have much to compare the flood style emitter too, but here's the Nitecore HC50 headlamp and a typical diffuser-covered light:
Basically, pretty much as you would expect, for a small reflectored light.
For outdoor beamshots, these were done using the standard location and setup as my earlier 100-yard round-up review. Please see that thread for a discussion of the topography (i.e. the road dips in the distance, to better show you the corona in the mid-ground).
As you can see, two completely opposite patterns are given by the two emitters – with the throw emitter lighting up the distance, and the flood emitter lighting up the foreground.
Understandably, you might like to see how things look with both emitters on Turbo. Unfortunately, I can't provide that right now – my original TK51 had a defective carrier with a severe current drain, limiting output when both emitters were run on max (although it was ok for the single emitter runs, shown above). By the time a replacement carrier arrived, there was already too much snow on the ground to take decent outdoor shots. For the time being, you will have to rely on the indoor beamshots above (taken with the replacement carrier). For more info on the initial fault, scroll down to post #2. I will try to remember to update this thread when Spring arrives …
How do the throw emitter compare to other lights?
The two lights above both have similar max output levels (with similarly-sized reflectors). As you can see, the TK51 Throw emitter is a bit more focused for throw than those lights – although the difference isn't huge.
All my output numbers are relative for my home-made light box setup, as described on my flashlightreviews.ca website. You can directly compare all my relative output values from different reviews - i.e. an output value of "10" in one graph is the same as "10" in another. All runtimes are done under a cooling fan, except for any extended run Lo/Min modes (i.e. >12 hours) which are done without cooling.
I have devised a method for converting my lightbox relative output values (ROV) to estimated Lumens. See my How to convert Selfbuilt's Lightbox values to Lumens thread for more info.
Throw/Output Summary Chart:
My summary tables are reported in a manner consistent with the ANSI FL-1 standard for flashlight testing. Please see http://www.flashlightreviews.ca/FL1.htm for a discussion, and a description of all the terms used in these tables. Effective July 2012, I have updated all my Peak Intensity/Beam Distance measures with a NIST-certified Extech EA31 lightmeter (orange highlights).
Let's start by looking at each of the emitters separately, compared to standard 1x18650 lights:
The TK51 is certainly driving the individual emitters very hard on Turbo – these are among the highest readings I've seen for single XM-L2 emitters. Of course, the extra "oomph" from the 3x18650 cells helps. The above is very consistent with what you saw in the beamshots – the TK51 Throw emitter is a good performer given the reflector size.
FYI, I don't believe there is any actual max output difference between the two emitters on the TK51 – the extra ~40 or so lumens for the flood emitter is likely just due to extra reflections inside my lightbox/ceiling bounce setup. But to be consistent with my other readings, I've left things where I measured them.
Let's see how the TK51 compares to high-output 3x/4x18650 lights:
With both emitters on Turbo, the TK51 is again at the high-end of 2xXM-L/XM-L2 lights I've seen. In fact, it is pretty close to many of the older 3xXM-L lights. I would consider them the closest comparable.
I also note that Fenix's ANSI FL-1 beam intensity and beam distance measures (for the throw emitter) seem very accurate - exactly in keeping with my testing results.
Here are how all the levels compare to the official specs:
As you can see, my numbers are pretty much spot on with Fenix specs. My single emitter Turbo numbers are slightly higher (especially for flood), but I suspect that's just my calibration standard being slightly off – the two emitters add up to ~1800 lumens, so they really should be ~900 lumens a piece.
FYI, I can confirm that the output of each emitter singly doesn't change as you adjust the output of the other. So the Fenix specs of 900/1800 lumens seem very accurate. I recommend you stick with the official specs.
Let's start by a battery comparison, with both emitters on Turbo – with and without cooling:
As you can see above, there is thermal-mediated step-down of the TK51 when run on max output. Once the light steps-down it remains flat-regulated for quite some time. However, in the case of 3x18650 (AW 2200mAh Protected), my typical cooling fan was sufficient to prevent this step-down (and instead produced a consistent direct-drive-like pattern). Note that despite how this looks, the TK51 typically gives you at least a partially regulated pattern on 3x18650 – it is just sustained max output where regulation can't seem to be maintained (please see my additional runtimes below for more info).
It is not surprising that 6xCR123A always steps down (and faster than 3x18650) - even with a cooling fan. Due to the chemistry difference, resistance is higher on 2xCR123A than 1x18650 - and so CR123A get much hotter than 18650.
Let's see how a single emitter fares, when run on different numbers of 18650 cells. Not that for all remaining runtimes, these are done under a cooling fan.
The difference between 2x or 3x18650 cells is simply a question of how long the light can maintain regulation, and how long the cells will last. On 1x18650, the story is different – the TK51 cannot maintain max output on a single emitter for any length of time. As you can see above, initial output is slightly lower, and the cell runs in apparent direct-drive like pattern the whole time.
Let's start comparing the TK51 to the competition – beginning with typical 2x18650 class lights:
Clearly, the extra 18650 cell gives the TK51 a runtime edge over most of the 2x18650 lights shown above. So for a better comparison, let's look at higher capacity 3x/4x18650 class lights:
First thing I'll say is that the regulation on 3x18650 – on single emitter, or lower outputs of dual emitters – isn't that bad in practice. No, it is not fully regulated over the entire runs, but you are not able to notice the gradual drop off in output once it falls out of regulation.
The TK51 is a very efficient performer overall. Compared to other good quality current-controlled 3xXM-L lights on 3x18650 though, the TK51 is typically not quite as long-running – but that's because the 2 emitters here have to be run at higher currents to get equivalent output. It's always advantageous to have more emitters at lower drive currents when it comes to overall efficiency – but of course, beam pattern and throw is often compromised in multi-emitter setups.
There is a standby drain between the head and the carrier – as well as within each carrier well (due to an additional circuit inside the carrier). Although the combined drain is still pretty negligible (i.e., would be years to drain the cells), you would need to pull the cells from the carrier to block all current. There is no electronic lock out that I am aware of - although loosening the head from the body by at least a half-turn is sufficient to prevent accidental activation. Note that my original sample had a defective carrier with an unsually high drain (see post #2).
There is a thermal-sensor mediated step down when run on max output on both emitters (although step-down may be avoided if sufficient cooling is applied). This is superior to a timed step-down.
The TK51 is typically only partially regulated on 3x18650. This has advantages for overall runtimes though, as it means you get a gradual period of drop-off as the cells near exhaustion (i.e., not left in the dark without warning).
Although user interface is improved from some earlier TK-series lights , it may still not be ideal for all users.
Light is relatively large for the output levels.
The TK51 is certainly a distinctive build – I don't recall seeing side-by-side throw and flood-focused reflectors before.
Build quality is high, in keeping with the other TK-series lights from Fenix. You may find the TK51 a bit large for its overall output, if you plan to run primarily on just one emitter (or at lower levels on both). That said, the 3x18650 arrangement does provide for extended runtime, compared to smaller lights. And it also allows for each emitter to be driven to the maximum possible output level (i.e., Turbo on each emitter singly is slightly higher than a typical 1x18650, for example).
The battery carrier remains rather more "beefy" than most in this class, and is likely to be quite durable. However, I was surprised to find a circuit in there (see comments in post #2). Also, you may find longer 18650 cells to be a tight fit.
Consistent with other Fenix offerings, overall efficiency is very good. Regulation pattern is serviceable - although I expect some here would have preferred a more extensive fully-regulated period. Still, I find this to be a good compromise for the performance level (and you are never left in the dark without warning). Note that there is a thermal sensor in the TK51, which can trigger a step-down when both emitters are on in Turbo output. This is superior to a timed step-down, as the output can also recover if cooling is applied.
The user interface is updated from earlier TK-series lights. The use of two buttons for control of each emitter separately is intuitive (and improved over some of the earlier TK models). The dual control button is helpful, but I found myself wishing it would increase both emitters in lock-step (as opposed to simply turning on/off where ever you left each emitter, or jumping both to max momentarily). But of course, your preferences may vary.
Either way, the beam of the TK51 is very impressive. They have managed to get very good concordance of the two emitters when run together, and each is well suited to its specific role (i.e., optimized for throw, or flood). It's kind of fun to be able to control each emitter independently, leading to some neat effects.
The TK51 is an interesting approach to getting either throw or flood in one light – although to be honest, a well-designed diffuser cover can accomplish this easily on a traditional light. The distinctiveness here is the ability to control each emitter individually, leading to distinct combinations. Of course, while fun to play with in testing, I'm not sure how practically useful that is in real life. I'm curious to hear what others think of using this arrangement in the field.
P.S.: One point I would like to highlight - Fenix's ANSI FL-1 measures for output, beam intensity and runtime on the TK51 are all very consistent with my testing. Fenix clearly takes pains to provide the most accurate measures possible, relative to the requirements of the standard. I only wish other makers did as well!
TK51 provided by Fenix for review.