Fenix TK61 review

Posted by Zak Wilson on Oct 10, 2015

Fenix's TK61 is a serious tool for serious work. It's not the longest throwing thrower, but at 824 meters, it's not terribly far off.

History

The TK61 shares its body tube and battery carrier with the multi-emitter TK75. It was purpose-built as a dedicated thrower, and seriously overengineered for predictable extended use. If Olight's M3XS-UT Javelot is a hot-rod, the TK61 is a semi truck.

Philosophy of Use

The TK61 is not meant for casual use. This is a light for people who need to see long distances in the dark for extended periods of time. It's suitable for search and rescue, for certain police operations, use in conjunction with off-road vehicles when the mounted lights don't reach far enough or point the right direction and for sizing up situations in a farm, construction or outdoor industrial setting where fixed lighting is unavailable or not up to the task. This is a tool for serious work in part because of its quality and performance, but also in part because it's too bulky to carry casually. Without a dedicated space in a bag or on a vehicle, I don't see many people bringing a TK61 on an outing just in case.

Construction and Durability

The TK61 is solidly built. The annodizing is smooth and even. The machining is clean and precise. All soldering visible after lifting up the contact board to reveal the driver (may void warranty; not recommended) is clean and well-done. The reflector is plastic, not aluminum as in most other premium lights, but given the size, plastic makes sense for weight savings.

The TK61, like most Fenix products is rated waterproof to IPX8 standards, further specified as 2 meter submersion for up to 30 minutes. I tested waterproofing by putting the light in the freezer with the tailcap removed until it was cold-soaked, then sealing it and submerging it. As the air warms, it tries to escape. Some air is expected to escape, as lights are rated waterproof, not airtight, but the slower the bubbles come out, the better the seals. Barely any air escaped from the TK61. A few small bubbles formed very slowly near the buttons, and the light floated. When I opened the cap following the test, I could hear air escaping forcefully. This is one of the best sealed lights I've tested.

User Interface

The power button is a simple on-off toggle, though a long-press will activate a momentary high until released. The mode button cycles to the next mode - brighter unless high is already selected. Pressing and holding the mode button will activate strobe whether the light is on or off. Another long-press will activate SOS. A short press of the mode button from either flashing mode returns to the last-used constant mode. The last-used constant mode is always memorized for the next time the light is turned on, and flashing modes are never memorized. The momentary function is not well-suited to signaling with Morse code.

There is no way to lock out activation of the TK61 short of removing the batteries. The latest revision of the TK75 has an electronic lockout, and it would be a good idea for Fenix to incorporate this feature on the TK61. Nearly removing the tailcap may break the battery carrier's contact with the contact board, but isn't a particularly reliable lockout. I have had the TK61 activate inadvertently while carrying it in a backpack.

Modes

Standard modes are 20, 130, 400 and 1000 lumens. As human perception of brightness is roughly logarithmic, each mode appears approximately twice as bright as the last. Strobe is variable-rate and extremely disorienting, but the TK61 isn't really designed for self-defense applications otherwise, so I'm not sure how important this is. SOS is 130 lumens and likely has a runtime of a week or more.

The lowest mode has minimal utility. The hotspot is too small to be good for much up close, and the spill is too dim. The two medium modes are usable for lighting one's immediate surroundings walking outdoors. The highest mode is obviously most useful for the TK61's intended purpose: throw.

Beam

The hotspot is small, well-defined and bright, with a substantial corona. Both are a typical cool white around 6500K with no noticeable off-colors. The spill is wide and dim, though usable for basic tasks on higher modes. The only problem with the TK61's beam is that the spill is purple. While spill is not the point of a dedicated thrower, I think this could be mitigated with a daylight or neutral tint emitter, both of which could achieve the same level of output with no loss in efficiency. A different anti-reflective coating on the lens might also help make the spill a more useful tint. Human eyes are not especially sensitive to purple, so in addition to interfering with color reproduction, the spill appears even dimmer than it needs to be.

Ergonomics

The TK61 has a fat grip with mild raised texturing. It's easy to hold on to, and the buttons are raised and easy to press in both overhand and underhand grips. The grip should be comfortable and secure for most hand sizes. A shoulder strap is included, and is a comfortable way to carry the light during use.

Performance

Fenix's TK61 reaches out to long distances very effectively. It's not quite as impressive as Olight's M3XS-UT Javelot, but it can maintain full output as long as the batteries can handle it, while the M3XS-UT steps down after five minutes. To be fair, the M3XS-UT can be reset to full by cycling through modes, but having constant full performance with no signs of stress from the light is advantageous. The TK61 has no difficulties with heat. After an hour at full brightness, it's only comfortably warm to the touch, never hot. The cool tint does refract off of haze and airborne dust more than the warm tint of the M3XS-UT Javelot, but any thrower is going to produce a visible beam under such conditions.

The TK61 can run for four hours and twenty minutes on maximum using high-capacity 18650s before it steps down to a lower output to prevent damage to the batteries. Having batteries in series means there is no inherent loss of output as voltage drops. It will continue running at reduced output for some minutes after the stepdown. The caveat with series lights is that all batteries should be the same make, model, capacity and state of charge. If one battery is much lower than the rest, when the batteries get low, it can be subjected to reverse charging, which may cause it to vent corrosive gasses or even catch fire. Fenix recommends batteries with protection PCBs, which can usually prevent this condition. Even with protection PCBs, it is important to ensure the batteries match.

Safety

The manual states that there is a low-battery warning after the last stepdown in the form of intermittent blinking. I attempted to reach this warning using two Sanyo 18650s salvaged from a laptop battery, stopping on occasion to test voltage. At 5.0V total, I checked the cells individually and found one at 3.4V and the other at 1.5. This was well on its way to being a hazardous condition, and the low-voltage battery may already be unsafe to use. The blinking warning never appeared, and the total of 5.0V was already under the recommended minimum of 2.7V per cell for most Li-ion batteries.

Continuing to use the TK61 after it automatically steps down to the lowest mode presents a significant risk of over-discharging the batteries or even reverse-charging. It is potentially dangerous to recharge a Li-ion battery that has been over-discharged, and reverse-charging presents a significant immediate danger. Leaving the TK61 on and unattended or in a backpack with batteries installed increases the risk.

Most non-experts are better off using this light with protected batteries.

Accessories

The TK61 comes in a foam padded cardboard box and includes a manual, spare O-rings, a carrying strap and some paracord.

Sold separately are TK75 extended runtime kits and sealed USB rechargeable battery packs. Either will double the runtime. With two extended runtime kits, the TK61 can use up to 12 18650 batteries and run for 13 hours at full output.

Conspicuously absent from the accessories is any kind of holster or even a lens cap. It is difficult to protect the TK61's large glass lens from damage while carrying it in a backpack with other items. A well-designed holster would also help to prevent accidental activation. Fenix does not make one; the only option is to find a third-party holster.

Conclusion

The TK61 is a solid workhorse of a thrower. It will do exactly what it says on the box and fairly little to surprise the user unless it's carried in a bag with other items or used with unprotected batteries. This is one of the few lights I would strongly recommend most people use with protected batteries.

I wish I didn't have to add an extra warning about battery safety with this light. It's so foolproof and predictable otherwise. The necessary changes, an electronic lockout and a low-voltage cutoff between 6 and 7 volts could be done entirely in software.

Other lights to consider

The TK61 is a heavy-duty workhorse. That's not for everyone. If you're looking for something else in a long distance flashlight, you might be happier with:

Olight M3XS-UT Javelot - Olight's factory hot-rod out-throws nearly every off the shelf flashlight.
Fenix TK75 - like a TK61 with four emitters. It has slightly less range and obviously generates more heat and runs through batteries faster, but with 4000 lumens, it lights up a much larger area. Extended runtime kits work with this too.
Nitecore TM16 - very similar to the TK75, but people who have used both seem to prefer the Nitecore's user interface mode selection and the fact that it doesn't need a separate battery carrier. No extended runtime kits though.
Olight M2X-UT Javelot - like a smaller version of the M3XS-UT. It isn't hot-rodded quite so much and runs on a single 18650, but it nearly matches the TK61 in throw. An extension tube for a second 18650 is sold separately.
Olight SR52-UT Intimidator - the M2X-UT head on the SR Mini body. 3 cells and USB charging offer good runtime and convenience in a mid-size package.
Nitecore TM36 - one of the few handheld lights that can out-throw the M3XS-UT Javelot.

Pros

Great cooling
Excellent waterproofing
Long runtime
No reduction in output until the batteries are near-dead
Ideal mode spacing
Simple operation; easy to explain or discover experimentally
Very long throw

Cons

No lockout
Raised buttons can be accidentally pressed easily in a bag
Purple spill
Huge
Included accessories do not provide protection for the large, breakable lens during transport
Lack of a low-voltage shutoff makes use with unprotected batteries hazardous for non-experts

Specs

Max Output: 1000 lumens
Min Output: 20 lumens
Run Time (highest setting) 4h20m (with four 3400 mAh 18650 batteries)
Beam Distance: 824m
Peak Beam Intensity: 170,000 candela
Water Resistance: IPX8
Impact Resistance: 1m
Head Diameter: 96mm
Length: 216mm
Weight: 600g
Batteries (recommended): 4x18650
Batteries (backup): 2x18650, 8xCR123; use of RCR123, 16340, 18350 or other small Li-ion cells requiring two in series in each battery slot is not recommended