REVIEW: ThorFire TK18 Flashlight

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REVIEW: ThorFire TK18 Flashlight

The ThorFire TK18 is the newest light in the narrow-body, single 18650-using TK series.  Compared to the TK15 and TK15S, the TK18 is brighter, offers a ramping output UI, has an electronic battery indicator built into the side switch, has a more distinctive body pattern/knurling, and offers a temp closer to neutral.



Here are the key review details:



Skip to the commentary section at bottom to read my subjective notes on the TK18.


Disclaimer: This light was provided at negligible cost by ThorFire, shipping from an Amazon distribution center in the U.S.  Cost was $28.80 at the time the TK18 was provided for review.




The TK18 arrived in a simple brown box with white label.  This packaging design is common across the ThorFire lineup.  The TK18 is pictured on top; registration and disposal information, website, and contact information is on the side.



Inside the box we find the TK18 in a foam sleeve.  There is black foam underneath but none on top.  The manual is on top and the spare o-rings are packed underneath.



What’s included:



The manual is in English only. It covers specifications, features, UI, and troubleshooting well.



ThorFire backs the TK18 with a 40-day replacement warranty and an 18-month repair warranty.




The TK18 is a slim profile 18650-based flashlight – one of several that ThorFire offers.  The TK18 really stands out, thanks to the large diamond texture on the battery tube.  It’s also the only model to have an illuminated side switch or a ramping UI. 

L to R: TK15S, TK18, TK15, VG-15.



The bezels and reflectors of these models vary.

L to R: TK15S, TK18, TK15, VG-15.



ThorFire lists the length at 134 mm, width at 24 mm, and weight at 91 g.  My measurements confirmed these specs to the nearest mm/g.  The head is slightly wider than the body tube at 27 mm.


For a better size comparison, here is the TK18 with more ThorFire lights (and the batteries they use).

L to R: S70S (26650*2), BLF Q8 (18650*4), C8S (18650), TA-13 (18650/3xAAA), TK18 (18650), TK15S (18650), VG-15S (18650), TK15 (18650), TG06S (AA).


Disclaimer: I purchased the BLF Q8 and TA-13. The other lights were provided by ThorFire for previous reviews.



The head of TK18 has a crenulated stainless bezel. Some light machining marks are visible. The crenulations are not aggressive and does not make pocket carry painful.  If the TK18 is set head-down while powered on, light will escape.



I was unable to remove the bezel by hand; it is either glued in place or is just very tight.



The lens is AR-coated.  The reflector is a light orange peel texture.  The XP-L2 LED is centered well though not absolutely perfectly.



The head of the TK18 has a HOT logo aligned with the side switch and is circled by shallow cooling fins.  The area around the switch is octagonal with alternating concave and convex surfaces.  Below the switch is the ThorFire logo and TK18 model embossed in white.



The side switch is multi-function. It not only controls the output mode but also displays current battery charge.  When the battery is >3.4V, the switch is green.  Between 3.0 and 3.4V, the switch is orange (as shown above).  Between 2.8 and 3.0V, the switch flashes red. (I tested and confirmed the transition voltages.) 

The switch protrudes from the head and is relatively easy to find in the dark. It also has a good mechanical feel and produces a click that can be heard and felt. It gets warm but not hot while in use.



Rather than the traditional fine-pattern knurling found on other lights, the TK18 has a very nice looking large diamond pattern engraved into the body tube.  This has been seen on other lights before, but is atypical for lights in this price range.  The anodization was free of defects; any appearing here is actually just dust.



The tail cap has a dual-hole lanyard attachment point on one side.  This design allows a lanyard to be attached without compromising the TK18’s ability to tail stand.  The tail switch is a forward-clicky so momentary on is possible with a half-press.



The TK18 disassembles into 3 pieces: head, battery tube, and tail cap.  The threads are longer on the tail end than the head end.



The battery tube has anodized square-cut threads on both ends – so a partial turn of will mechanically lock the light out.  Lubrication is good on the threads but lacking on the o-rings.



Gold-colored springs are present on both head and tail ends. 










Pocket Clip

The TK18 is designed for head-down carry only, as the only space for the clip to be installed is on the tail end and the battery tube is not reversible.  The clip attaches very securely to the light – it’s quite tight to install and remove.  The clip grips pockets firmly.




The XP-L2 is a single die emitter so there’s no crosshair to deal with like with quad-die emitters.  The orange peel reflector and moderately deep reflector produce a hotspot with a wide corona and bright spill. 



Tint & Temperature

The color and CCT are specified by ThorFire at 5350-5500K and my tests support the rating.  I found the XP-L2’s hotspot was neutral with a slightly yellow corona. The spill had a faint amount of blue.  Temperatures measured varied from 5000K to 5500K, with the spill unsurprisingly being the coolest.


To demonstrate the overall color balance, here is the TK18 surrounded by lights with emitters of various tints and temperatures on lower output modes.  Camera W/B set to daylight.

L to R: Convoy S2+ (cool XM-L2 U2 1B), Olight S1R (cool XM-L2), ThorFire TK18 (XP-L), Lumintop Tool Cu (warm 219B), BLF348 (neutral 219B SW50 R9050).



Getting a balanced output was difficult between the lights, so here’s one with the TK18 on a lower mode.  It demonstrates the slight yellowness of the corona around the neutral hotspot.



And here’s one more with a neutral tint (4300-4500K) Convoy S2+ thrown in.

L to R: Convoy S2+ (cool XM-L2 U2 1B0, ThorFire TK18, Convoy S2+ (neutral XM-L2 T6 4C), BLF 348 (neutral 219B SW50 R9050), Lumintop Tool Cu (warm 219B).





Thorfire rates the TK18 at 1200 lumens on Turbo when powered by a 3000mAh ThorFire cell.  I tested first with an unprotected Samsung 30Q cell and found turn on output of 1028 lumens. Output at 30 seconds was an even 1000 lumens.


I noticed when reviewing other ThorFire lights recently that using an ultra- high-drain cell like the 30Q doesn’t benefit performance as much as using a long cell that compresses the springs more and shortens the electrical path.  The Samsung 30Q is only 66.6 mm long so I tested again with a protected Nitecore NL1834 cell measuring 69.6 mm and found output was improved with turn on at 1072 lumens and 1046 lumens measured at 30 seconds.  Using an even longer cell – or performing a spring bypass mod – should improve performance further.


The full runtime was tested using the 30Q since it has the same 3000mAh capacity as the recommended ThorFire cell.


ThorFire states in the manual that there is a stepdown at 3 minutes when in Turbo mode or over 80% to prevent overheating and save power.  With the 30Q, I found the TK18 was outputting 973 lumens at 3 minutes 22 seconds – then quickly stepped down to 395 lumens a second later.



From there, output declined in a linear manner. ANSI runtime (based on 10% of initial measured output) was reached at 4 hours 25 minutes.  This exceeds ThorFire’s 45 minute rating dramatically. The TK18 eventually powered off at 5 hours and 2 minutes.



Ambient temperature was 70F (21C).  Max temperature measured was 114F (46C) at the head, 101F (38C) at the battery tube, and 98F (37C) at the tail. 



ThorFire rates High at 500 lumens and 2 hours 30 minutes.  I measured 430 lumens at 30 seconds with the Samsung 30Q battery.  Output at 5 minutes was 417 lumens and from there the output declined in a linear and predictable manner.  Output was down to 54 lumens at 5 hours 6 minutes – when the TK18 powered off.  This runtime also exceeds ThorFire’s 2 hour 30 minute rating dramatically.



Medium is rated by ThorFire at 100 lumens for 10 hours. I measured 120 lumens at 30 seconds using the 30Q. Again, output declined gradually and consistently. 50% output was reached at 12.5 hours.  10% output was reached when the TK18 turned off from 14 lumens at 20 hours and 42 minutes.



Low is rated at 3 lumens and 100 hours.  I measured 5.8 lumens.  Output was not tested.


In ramping mode, peak output was the same.  However, minimum output in ramping mode was lower than Low in stepped mode.  Minimum in ramping was 1.8 lumens – down from the 5.8 measured in Low.



All outputs (set steps):



All runtimes tested:



Amperage Draw

As measured with fully charged Samsung 30Q cell:

  • Turbo: 2.7A
  • High: 0.78A
  • Med: 0.22A
  • Low: 10.5mA




I tested throw distance at 1.41 meters and the resulting candela was 7913 at 30 seconds - equivalent to 171 meters of throw.  ThorFire does not specify Cd or throw in the manual.





The TK18 appears to have PWM on all modes except Turbo/100%.  I was able to detect it at all lower modes using a camera’s CMOS sensor.  That said, it was fast enough that I was not able to see it with my eyes in normal use or with the “mirror test”.




Parasitic Drain

As the TK18 uses a mechanical tail switch, there is no parasitic drain when off.




Low Voltage Battery Protection

The TK18 manual states that the TK18 will power off when the battery reaches 2.8 V – and it does just that.  After runtime testing, I let the cells rest before testing – and measured 2.89 to 2.93 V.  This is in line with a 2.8V cutoff voltage and makes it safe to use a variety of unprotected cells.



Impact Resistance

ThorFire rates the TK18’s impact resistance at 1 meter.  This was not tested.



Outdoor Beamshots

All photos taken with a Canon SD4000IS camera. 1/4" exposure, ISO800, Daylight white balance, F2.0. Approximate distances: White deck railing @ 15 ft., white fence in distance @ 75 ft, back of dock @110 ft.

(For those that wonder… an ice flow turned my hoist sideways.)



















The TK18 has two modes – ramping and stepped.

Pressing the side switch 4x while on switches between the modes.

Mode memory is present in both.


From off:

  • Half press the tail switch to momentarily turn the TK18 on.
  • Full press the tail switch to turn the TK18 on.


From on, Ramping mode:

  • Press and hold the side switch to increase output power.
    • Main emitter will flash when at 100% (min to max takes 7.5 seconds).
  • Press, release and press side switch again in under 1.5 seconds to decrease output power.
    • Main emitter will flash when at lowest level (max to min takes 7.5 seconds).
  • Press side switch 3x quickly to enter Bike Strobe mode.
    • Press side switch again to return to last used normal output level.
  • Press side switch 4x quickly to switch UI to stepped outputs.
  • Press tail switch to turn off.


From on, Set Stepped mode:

  • Press side switch to switch output level.
    • Cycle is up then down, L->M->H->T->H->M->L.
  • Press side switch 3x quickly to enter Bike Strobe mode.
    • Press side switch again to return to last used normal output level.
  • Press side switch 4x quickly to switch UI to stepped outputs.
  • Press tail switch to turn off.





No problems were experienced with the ThorFire TK18 while testing.





The TK18 is the best single 18650 light I’ve tested from ThorFire.  The tint is pleasant. The ramping UI makes it easy to find just the right output. The illuminated switch makes monitoring battery state easy.  It has momentary on and no parasitic drain. The large diamond pattern on the battery tube looks classy.  There’s really a lot to appreciate given the $29 price point.


Output as tested didn’t achieve the 1200 lumens advertised, but there are ways of achieving more output with minor modifications.  In reality, the difference between 1050 and 1200 lumens is not noticeable for most people.  Users will notice that the runtimes are much longer in real-world use than in ThorFire’s specifications – a welcome surprise.


The only things I’d really change on the TK18 is the ramping speed and the lack of access to minimum output in stepped mode.  7.5 seconds is pretty slow to ramp up or down and there’s no double-click to Turbo or other shortcut to speed that up.  It’s also a little odd that ramping can access a lower low than while in stepped mode; the addition of a 5th stepped level could solve this problem.


Overall the TK18 is a great value and a worthwhile upgrade from the TK15/TK15S.


Lux Meter: Dr. Meter LX1330B
Integrating "sphere": Homebuilt tube-style device calibrated on other known lights and test results. Numbers should be considered relative to each other and my other review figures but accuracy is in no way certified or guaranteed.
Camera: Canon SD4000IS
Micrometer: Mitutoyo CD-6ASX
Multimeter: Craftsman 82170

Edited by: bdm82 on 01/29/2018 - 23:31