Warning: even more pic heavy than usual.
Reviewer's Note: This is my first review of custom modified light – in this case, from the well-known CPF modder Vinh Nguyen. For more information on Vinh's lights, please check out the vinhnguyen54 subforum of the CPF Custom Flashlight Builders and Modders forum.
The TK61vn is currently the farthest throwing reflector light that Vinh makes. He has sent me a sample of his top-line TK61vn model, with the 6500K Dedome PDT ("premium dedome tint"). See the spec descriptions for more info on what that all means.
Again, this is a full review of a modified TK61 (known as the TK61vn). While not intended to serve as a review of the stock TK61, I have picked one up to provide direct output/throw/runtime/beamshot comparisons. Given that the physical build is pretty much the same for external appearances, you should be able to figure out everything you need to know about the stock TK61 from this review as well.
For more information about the TK61vn specifically, please see Vinh Nguyen's TK61vn discussion thread here on CPF.
Let's see how the modified TK61vn compares to the stock form, and to other high-output throwers in my collection.
Stock Fenix TK61 Reported Specifications:
- LED: Cree XM-L2 (U2)
- Uses four 18650 rechargeable Li-ion batteries or eight CR123A Lithium batteries
- Output mode / Runtime:
- Turbo: 1000 lumens / 4h 20min
- High: 400 lumens / 14h
- Mid: 130 lumens / 46h
- Low: 20 lumens / 300h
- Strobe: 1000 lumens
- SOS: 130 lumens
- Beam Distance: 824m
- Beam Intensity: 170,000cd
- Digitally regulated output - maintains constant brightness
- Reverse polarity protection, to protect from improper battery installation
- Over heat protection to avoid high-temperature of the surface
- Dual switches on the head 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
- Impact Resistance: 1m
- Waterproof: IPX-8, underwater 2m
- Dimensions: Length: 8.5" / 216mm, Body Diameter: 2.07" / 52.5mm, Head Diameter: 3.8" / 96mm
- Weight:21.12oz / 600gm
- MSRP: $160
Vinh Nguyen TK61vn Reported Specifications: (where different from above)
- LED: XM-L2 6500K Dedome (see other options below)
- Output mode: Test Done by CPF Member rdrfronty
- Turbo (30 sec.) - 1735 lumens
- High - 840 lumens
- Medium - 332 lumens
- Low - 53 lumens
- Beam Distance: 1577m
- Beam Intensity: 622,000cd
- Factory 3.1A boosted to 5.75A
- Battery carrier tweak
- Tune for best focused beam
- New electrical components added to handle high current draw
- Crucial high heat electrical components cooled with thermal pad
- Light will get uncomfortably hot around 10 minutes. Please throttle down at this point.
- Price / Options:
- 6500K Dome On $240
- 6500K Dedome $255
- 6500K Dedome PDT $270 (Reviewer's note: this is the sample reviewed here)
- 4500K Dome On $250
- 4500K Dedome $255
Note: As always, these specs are simply what Fenix and Vinh Nguyen provide – scroll down to see my actual testing results.
Packaging is fairly standard for Fenix. The large cardboard box has key performance and use specifications printed right on the outside. Inside, in sturdy packing foam, you will find the light, extra o-rings, basic should strap, simply wrist lanyard, manual, and product inserts. As you can see in the opening pics to this review, my TK61vn came with a little thank you note from Vinh as well.
From left to right: AW Protected 18650 2200mAh; Fenix TK61vn, TK75; Fenix TK51; Niwalker Vostro BK-FA01; Thrunite TN35.
All dimensions directly measured, and given with no batteries installed (unless indicated):
Fenix TK61vn: Weight: 608.0g (792g with 4x18650), Length: 218mm, Width (bezel): 96.0mm
Fenix TK61: Weight: 605.7g (790g with 4x18650), Length: 218mm, Width (bezel): 96.0mm
Fenix TK75: Weight: 516.0g (700g with 4x18650), Length: 184mm, Width (bezel): 87.5mm
ArmyTek Barracuda (XM-L2): Weight 400.8g, Length 264mm, Width (bezel): 64.0mm
Eagletac MX25L2 Turbo (SBT-70):Weight: 698.6g (with battery pack: 974.1g), Length: 292mm, Width (bezel): 91.3mm
Niwalker BK-FA01 (XM-L2): Weight: 682.3g (864g with 4x18650), Length: 209mm, Width (bezel): 80.0mm, Width (tailcap): 50.3mm
Olight SR95S-UT (SBT-70): Weight: 1,208g (with battery pack), Length: 323mm, Width (bezel): 87mm
Olight SR95-UT (SBT-90): Weight: 1,221g (with battery pack), Length: 323mm, Width (bezel): 87mm
Skilhunt K30-GT (SBT-90): Weight: 635.9g (773g with 3x18650), Length: 199m, Width (bezel): 76.0mm
Thrunite TN32 (XM-L2): Weight: 655.9g (808g with 3x18650), Length: 201mm, Width (bezel): 79.0mm
As you can see, the overall design is reminiscent of the multi-emitter TK75 – only with a much larger head for that deep-throwing reflector.
The TK61vn is a substantial light, with a solid look and feel. As with other recent TK-series lights, anodizing is a flat black, and seems in very good shape on both my stock TK61 and TK61vn. Whatever modifications Vinh has done to the light, he has not marred the finish on my TK61vn.
Stock TK61 body labels are fairly minimal, but clearly legible (except for the temperature warning, which is oddly printed on an uneven region). Again consistent with the TK-series, there is no knurling per se on the light. However, the checkered pattern on the handle has been updated, and is raised compared to earlier TK-series lights (helping considerably with 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.
There is a shoulder attachment strap ring located in the head area (that rotates around). Combined with the attachment points in the tailcap, you should be able to carry it securely in this fashion.
The TK61 can tailstand stably, thanks to its raised cutouts. As you can see on my TK61vn, Vinh has done a nice job hand-engraving his logo. This is the only obvious indication that the light has been modded (well, aside from the dedomed emitter – but we'll get to that).
The TK61 uses electronic switches in the head to control on/off and mode switching. The right switch controls on/off, and the left controls output level selection. Switch feel is good, and there is a definite "click" when making full contact. Scroll down for a discussion of the user interface.
Inside the head, the circuit board is clearly visible there are two contact rings for the positive and negative current paths of the carrier. Again, no obvious signs that my TK61vn has been dissembled and rebuilt. The contact points in the stock TK61 look more robust than my earlier TK75.
Let's look at the carrier (from the modded TK61vn):
Here you can see some of the first signs of Vinh's modifications. Note that the stock TK61 carrier looks the same as the TK75 that I recently reviewed (see that review for stock pics).
I can see that Vinh has added an additional contact path inside each carrier well spring, soldered at the base and tip of the springs (likely to ensure good consistent current flow). This must be part of the "carrier tweaks" Vinh refers to. There was also been some red permanent marker transfer to the white carrier body (likely from cells that were previously installed – I cleaned most of these off with a bit of alcohol).
In general terms, the TK61/TK61vn carrier plastic is nice and thick, with a sturdy feel. The bays appear wide enough to accommodate a wide range of cell diameters, and I had no problem fitting the loaded carrier into the light with any of my cells. You may find longer cells a bit tight in the carrier, however. The raised contact disc at the positive terminal means flat-top cells will work fine. As before, I like the slight cut-outs near the positive terminals, to facilitate getting your cells out.
The carrier is organized in a 2s2p arrangement. This means that you could easily run 2x18650 cells in a pinch, as long they as they were located in adjoining cells to appropriately complete a circuit (i.e., side-by-side bays, with one pointing up and the other pointing down, as indicated by the carrier).
I STRONGLY recommend against trying to run the TK61vn on anything but the full complement of 4x18650, given how heavily driven this modified light is (although I suppose 2x IMR 18650 may be able to handle it). On a stock TK61, you should be able to get away with 2x18650 more easily.
The TK61 also supports 8xCR123A (and could probably handle 4xCR123A in a pinch). Again, I recommend exercising common sense with the modded TK61vn – the light and cells will heat up on Turbo, so sustained runtime on CR123A is NOT recommended.
Let's take a look at the head of my dedomed TK61vn:
Vinh sent me an example of his XM-L2 "premium dedome tint (PDT)", which he estimates to have ~5000K color temperature. As you can see in the pics above, dedoming the emitter gives you a clear view of the underlying die.
For a comparison, here is what the stock TK61 XM-L2 emitter looks like, with the exact same magnification as the last pic above:
The presence of the stock dome distorts the view of the emitter, of course, greatly magnifying it. Note that the emitter die centering was perfect on my TK61vn, and was only "good" on my stock TK61 (i.e., not perfectly centered, but not bad). This is again one of the benefits on a custom mod – everything is adjusted for absolute best performance.
Note that dedoming will improve peak beam intensity, but will likely also shorten the lifespan of your emitter.
The smooth reflector is massive on the TK61, which explains its outstanding throw. Some "tuning" of the focusing is done to maximize throw on the TK61vn (which I presume means some adjustment of the positioning of the reflector). There is a good quality anti-glare coating on the lens of the light (unchanged). The light also has a scalloped bezel ring,
Scroll down for beamshots.
Similar to the TK75 (but updated slightly), the TK61 uses two electronic switches to control on/off and mode selection. These are located just under head. The right button is the main On/Off switch, the left button is the output mode selection switch.
For constant on (or off), click the right power switch. A new feature on the TK61 is that you can also press-and-hold the power switch from off for momentary access to Turbo (more on this below).
When in constant on mode, click the left button to advance through the output modes. The TK61 has four main output levels, accessed in repeating sequence: Lo > Med > Hi > Turbo. The light has output level memory, and will come back on at whatever level you last turned it off in.
The light also has strobe/SOS modes, but these are "hidden" away from the main sequence. To access these flashing modes, press and hold the left button. If you hold the button down for ~2 secs, you will get a tactical strobe mode. If you hold the button down for >4 secs, you will get a lower output SOS mode. Release the left button to select your flashing mode (i.e., locked on). You can click the left button to return to the last constant output mode (or turn off/on by the right button). There is no mode memory for the flashing modes.
As with the TK75, you can access the strobe/SOS modes from off by pressing and holding the left button. But new on the TK61 is the ability to jump to a true momentary Turbo mode by holding down the right power button from off (i.e., press for momentary – release, and it turns back off).
However, as many others have reported here on CPF, some TK61 samples are variable in how long they will let you stay in momentary Turbo, even on fresh batteries. The light is supposed to stay on as long as you hold down the power button. But on my TK61vn, the light shuts off anywhere after 1-10 secs (despite continuing to hold down the power button). My stock TK61 does a little better, between 3-25 secs before randomly shutting down. Cause is unknown, but it doesn't affect any other function of the light. As a potential workaround for those affected, holding down the mode button once in momentary (and then releasing the power button) allows you to maintain an indefinite momentary Turbo (until you release the mode button). I presume Fenix is working to fix this particular bug.
For more information on the overall build and user interface of my TK61vn, please see my video overview:
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.
There is no sign of PWM on any level – I believe the TK61 is current-controlled, like other Fenix TK-series lights. I did detect some low-frequency oscillations on Lo/Med/Hi (but not Turbo):
Note that circuit noise is common on many current-controlled lights, and has nothing to do with the modification here. It does not affect performance, nor is it detectable visually. As per my usual review policy, I simply report on all circuit features that I can detect – it doesn't mean they are significant in use. Rest assured, the TK61/TK61vn are flicker-free in use, at all levels.
As with other Fenix TK-series lights, strobe is an oscillating frequency strobe, switching between 6.5Hz and 15.3Hz on my sample. Each frequency lasts for about ~2 secs. Here is a blow-up of each strobe frequency individually:
Strobe pulse width is a little unusual, but it doesn't really change how disorienting this strobe is.
Due to the electronic switch, the TK61 will always be drawing a small current when the carrier is connected to the head. I measured this current as 1.2uA on my stock TK61 sample. On my TK61vn, it was too low to get a reliable DMM reading.
As a result, the standby drain is completely negligible (i.e., it is well below the normal self-discharge rate of Li-ions). Note that like on the TK75, the carrier is in a 2s2p carrier arrangement.
However, you are not easily able to lock out the switch to prevent accidental activation. There is no electronic lock-out on this model, and unscrewing the head doesn't help much (i.e., it is the tension on the springs in the carrier that makes contact). You need to unscrew the tailcap several full turns to reliably lock out the light.
And now, what you have all been waiting for. All lights are on their standard battery, or AW protected 18650 2200mAh for the multi-18650 lights. Lights are about ~0.75 meter from a white wall (with the camera ~1.25 meters back from the wall).
Automatic white balance is used on the camera, to help minimize tint differences.
Rest assured – my TK61vn is not green in real life! It is difficult to accurately capture tint using a camera's auto white balance. That said, the dedomed PDT TK61vn is indeed warmer than cool white. I would say Vinh's ~5000K estimate is pretty good (on Turbo) – I would describe it as "creamy yellow".
Note however that for current-controlled lights, the tint shifts further to the warm end of the spectrum at the lower drive levels. This characteristic is exacerbated by dedoming. I do find indeed find my TK61vn to be slightly green at the Lo/Med levels (not noticeable on my stock TK61).
As for the beam, it's obviously hard to tell much at such ridiculously close distances. The tint difference also makes it hard to compare overall output in these pics - in real life, the TK61vn is definitely brighter overall.
As for the throw, it is hard to draw too many conclusions from these pics. Even at the maximum shutter speed of my camera, the hotspots are over-saturated. But you can probably tell that the TK61vn is more sharply focused (i.e., more defined hotspot edge, with less corona). To tell more, we are going to have to go out to further distances ...
Here are some indoor shots in my basement. For your reference, the back of the couch is about 7 feet away (~2.3m) from the opening of the light, and the far wall is about 18 feet away (~5.9m). Below I am showing a couple of exposures, to allow you to better compare hotspot and spill.
Let's see how the TK61vn compares to the stock TK61, and my more recent 1xXM-L2 throw champ, the Thrunite TN32.
Ok, that makes it a lot clearer – the TK61vn has MUCH greater peak hotspot intensity than either the stock TK61 or TN32.
The stock TK61 is fairly close to the peak intensity of TN32 (although the TN32 definitely has more overall output).
As you can also tell above, the TK61vn has more output overall, relative to the stock TK61. The camera's automatic white balance is also doing a better job of capturing the "feel" of the tint difference – but I caution again that these are never wholly accurate on a camera.
Of course, you would not be buying this light to explore the inside of your house. I need to do outdoor beamshots, but the snow has only finally melted this week. Give me a couple of weeks, and I'll update this thread with beamshots.
UPDATE May 17, 2014: Weather conditions have finally improved enough to start taking outdoor beamshots around here. To start, here is a comparison of the TK61vn to the stock form and the Thrunite TN32. I plan to add additional comparisons over the comping weeks, as I bring out some new lights to test.
As always, these are done in the style of 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, the V54 mod and dedoming hugely increases center-beam throw. You can see why this build was a good choice for this mod, as even the stock TK61 has a very focused beam. As you can also tell from above, the stock TN32 has greater output than the stock TK61 (this is another selling point in favor of the V54 mod, as overall output similarly increases).
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).
Ok, here's the top line: my TK61vn has ~600,000cd by ANSI FL-1 measures, making it the furthest throwing reflector light I've ever tested.
The stock TK61 came in right on the nose of the official specs, at ~170,000cd. This means that the modifications done by Vinh have increase peak beam intensity to 3.5 times the stock light (i.e., a 250% increase over the stock beam). Since light decays by an inverse square law, that means that beam distance has not quite doubled (but it is close to that).
The TK61vn has a remarkably tight (i.e., small) hotspot at 10m (which the ANSI FL-1 testing distance). It is possible that a further distance could provide more reliable indicators for such heavy throwers, but I have not personally experimented with non-ANSI measures.
Let's look at overall output:
As always, I don't insist on the absolute value lumen estimate for these large lights (since they don't fit in my calibrated lightbox). But my estimation method is consistent for relative output across all my reviews. And as you can see above, my method gives me a nearly perfect concordance with Fenix's specs for my stock TK61 sample. As such, I trust that my measures of the TK61vn are relatively consistent.
I also note that my direct throw measures and lumen estimates on Turbo are slightly lower than those reported in Vinh's TK61vn thread (as measured by rdrfronty here). But the difference is not great, and likely fits well within natural variation among modded lights. Also, Vinh informs me that rdrfronty had a "Factory LED Dedome", which would have been cooler tint than my sample. While that should not affect peak beam intensity, there may be some variation in lux meter sensitivity to different tint ranges. Again, my throw measures are done with a NIST-certified light meter under ANSI FL-1 testing conditions (i.e., working back from 10m). And ~600,000cd is an outstanding result under those conditions.
To look at it another way, that's a 250% increase in throw on my TK61vn, with only a ~65% increase in overall output, from stock.
Since the modded TK61vn is driven harder at all output levels - and there is no automatic thermal step-down on this model - Vinh recommends throttling down manual after ~10 mins of continuous runtime on Turbo. This is a reasonable precaution to me, as the light will get warm by this point.
All my runtime testing is always conducted under a cooling fan, for safety and consistency reasons. Surface temperature of the TK61vn remained reasonable after 10 mins of continuous Turbo runtime in my testing (i.e., never exceeded 47 degrees C surface temp at the hottest point at the base of the head). Nevertheless, I decided to follow Vinh's stated recommendations, and paused the Turbo runtimes after ~10 mins runtime. Once the TK61vn had re-cooled back to room temp, I restarted the runs. I have edited the traces below to only show you the "on times", with a spike at off/on time points. This should give you a pretty good idea of what continuous runtime would be like, should you attempt it (against advice).
As you would expect, overall output/runtime efficiency is not affected by the mod. The difference is in how much brighter the TK61vn is at each level.
The TK61 shows a clear step-wise step-down regulation pattern as the batteries drain. This is a convenient way of letting you know when it is time to change cells (well, when running at higher outputs at any rate). Regulation is very flat-stabilized.
In the case of the Turbo mode run, I got a little over half an hour before the TK61vn stepped down to Hi. Note again that I paused the runs at each the spikes above (pause time not shown), to allow the light to cool.
Let's see how it does against the competition …
The TK61 is a very efficient current-controlled light for this class – as is the TK61vn. The Thrunite TN32 remains the most efficient example I've seen to date, though.
General TK61 Potential Issues
The TK61 lacks any sort of electronic lock-out mode, and a physical lock-out requires several turns of the handle (to break the tension on the carrier springs). While not a concern for standby drain (which is negligible, well below the self-discharge rate of the batteries), lack of a robust lock-out is a potential issue for accidental activation.
My TK61 samples are inconsistent in the momentary Turbo feature (as has already been reported here on CPF). This was a new feature added to the TK-series, and it looks like Fenix still has some bugs to sort out.
The included shoulder strap/lanyard accessories are very basic. Despite the size, I expect most users would like a good quality holster.
Noticeable warm tint-shifting is possible at lower output levels on all current-controlled lights. I have commonly found a fair of amount of noticeable green tint on the lowest modes of many Fenix XM-L/XM-L2 lights. However, my stock TK61 was quite cool-tinted on Turbo (with a slight purplish hue), and I didn't notice anything significant when downshifting in this case.
TK61vn Potential Issues
The TK61vn is driven harder at all levels, so care should be taken not to overheat the light by sustained runtimes on Turbo (i.e., there is no built-in thermal step-down on this model series). If the light feels uncomfortably warm, you will need to throttle down manually.
Typically, dedoming an emitter tends to produce a warmer overall beam tint. The "premium dedome tint (PDT)" version of the TK61vn guarantees a more consistently neutral ~5000K tint on Turbo. However, my PDT version had a noticeable green-tint when downshifting levels (especially on Lo/Med). Vinh informs me that this green tint shifting is typically worse on non-PDT dedome versions (which usually have a cooler white tint to start with on Turbo).
Long-term reliability of any modded light is unknown, but it stands to reason the modifications for maximum performance here could shorten component life span (especially on the dedomed version). That said, Vinh also shores up a number of circuit components during his mods, which may increase overall useable lifespan of the light. Of course, modding voids all manufacturer warranties, but I understand that Vinh stands behind his products.
The TK61vn is the top-throwing reflector light I've tested to date, bar none. ~600,000cd is an incredibly beam intensity.
The stock TK61 from Fenix is good thrower light in its own right, with consistently accurate specs and performance. As with most of the Fenix line, the TK61 has flat stabilization (regulation) at all levels, with excellent output/runtime efficiency. It is also one of the "throwiest" XM-L2 lights in stock form, second only to the Thrunite TN32 in my testing. If Fenix could have driven the emitter as hard as the TN32, I have no doubt the TK61 would have overtaken the stock XM-L2 on throw.
Which brings us around to why this is such an attractive build for modding.
With some circuit tweaks to boost current – supported by upgrades to the circuit/carrier wiring and additional heatsinking – you would have the potential to push the TK61 much further. This is basically what Thrunite did on its TN32 model – they upgraded the standard TN31 components to produce the top stock XM-L2 throw king.
Of course, a custom mod can always do more than what a factory-produced light is capable of. A good example here is dedoming the emitter. When done carefully, this has the potential of greatly improving peak throw. A custom mod can also tweak the reflector focusing of each sample, for maximum throw. Put that all together, and I think you can see why conditions are ripe for some expert modification and enhancement on the TK61. Enter the TK61vn reviewed here, modded by CPF user vinhnguyen54. Vinh has a large following in the modders forum, and the TK61vn is currently his furthest throwing mod.
How well does this light throw? Well, peak beam intensity is ~3.5 times the stock TK61. That corresponds to ~3 times the stock TN32, and more than twice that of my previous peak throwers, the SBT-70-equipped Olight ST95S-UT and Eagletac MX25L2 Turbo. As an aside, the SBT-70 is almost like a factory-dedomed SST-90 (only with a thin protective covering, and rounded die edges for improved focusing). But the smaller die XM-L2 – when dedomed - has a definite edge when driven to the same overall output level.
So what is the downside to doing this? Well, modding obviously voids all manufacturer warranties, and tweaking all the components may shorten their lifespans (although by the same token, Vinh also upgrades internal components, and corrects potential stock issues). There is presumably a reason why LED makers install a dome over their emitters in the first place - part of it is esthetics (i.e., beam pattern artifacts and tint shifting are reduced by the dome), but part of it may be long-term reliability and stability of the emitter. That said, in my experience the vast majority of LED flashlight failures are due to circuit components, not emitters - and I understand that Vinh stands behind his mods. In any case, I suppose none of that matters for those looking for the ultimate thrower hot-rod – zoom, zoom.
Output/runtime performance of the modded TK61vn remains excellent – all that has really changed here is the drive level of each mode, and the amount the beam throws. See the tables, figures and beamshots in this review for a comparison.
Please check out Vinh's TK61vn discussion thread here in the modders forum for more info on this light (and tons more beamshot comparisons). If you are comfortable going the modded light route, the TK61vn is the clear throw king in my testing at the moment.
TK61vn was provided by Vinh Nguyen for review. Stock TK61 was purchased from a local vendor.