The TK75 is Fenix’s first 2500+ lumen light to be powered by 18650s and (as far as I am aware) the first light of its type to have battery tube extensions (each holding 2 or 4 additional 18650s) for extra runtime. This special ‘extended runtime’ feature is examined in detail after the main review.
The TK75 replaces the TK70, and in its base form is significantly more compact as it runs on four 18650s rather than 4 D-cells.
This is the fourth of a series of four detailed reviews of a selection of lights making up the ‘Totally Fenix Hunting Line-Up’. Included in the series are the TK22 (Reviewed here), TK15 S2 (Reviewed here), HL30 (Reviewed here), and this, the TK75, all of which provide a rounded set of capabilities covering everything you would need while out hunting.
Of course each of these lights stands perfectly well on their own, so this review will be covering the light in its own right, and following the individual reviews there will be a follow-up review covering the hunting applications.
Having used the TK45 and TK41 previously, the TK75 presents itself as the grown up older brother. Arriving in the familiar plastic case, having similarly solid build quality and using the sidewinder dual switch, the TK75 just lifts the Fenix TK range to the next level.
Like the recent TK22 (reviewed earlier) the TK75 uses a stainless steel bezel giving it a serious look and more robust light head. The size of head provides a good mass of metal for heat sinking and incorporates a generous compound reflector array for the three XM-L U2 LEDs.
Fenix build quality is clearly evident with flawless fit and finish. The TK75 certainly lets you know it is a serious lighting tool.
What is in the box:
Surrounding the TK75s plastic carry case is a cardboard sleeve.
Sliding off the sleeve, reveals the single piece moulded plastic carry case which incorporates a handle.
The design uses a ‘living hinge’ to join the two halves of the case.
Included in the case are the TK75, 2 spare o-rings, a lanyard and the instructions.
Taking a closer look and looking inside:
The TK75 uses Fenix’s Sidewinder dual button electronic switch interface which places the controls comfortably under the user’s thumb.
The model, serial number and other information are laser etched into the anodised surface.
Looking into the compound reflector shows how Fenix have filled the available space with an array of good sized reflectors.
The reflectors also have a reasonable depth which provides better focusing of the beam.
The three emitters are XM-L U2 LEDs.
Threads are perfectly finished, fully anodised, lubricated and the typical trapezoid profile seen on most Fenix lights.
The tail-cap design has plenty of lanyard attachment points and provides a very stable platform for tail standing.
The TK75’s battery holder is a unique, stackable design. The main output contacts consists of a coil spring positive contact and a set of four leaf spring negative contacts
On the tail end of the battery holder is a set of contacts just like those found in the TK75’s head. These provide a connection point allowing for stacking of additional battery holders if using the extended runtime kits.
Inside the battery holder are the individual cell contacts with coil springs for negative contacts and button contacts for the positive terminals. The battery holder has a 2S2P cell configuration.
Shown here loaded with four Fenix ARB-L2 18650s.
The inside of the tail-cap has no insert and is simply a plain anodised finish.
Removing the battery tube allows a clear view of the positive and negative terminal contacts for the light head.
The TK75 breaks down into four main components, the head, battery tube, battery holder and tail-cap.
The compound reflector’s finish is excellent. The stainless steel bezel is gently crenelated.
Modes and User Interface:
The TK75 has four constant output levels and two flashing modes.
A single press of the right hand button will turn the TK75 on and off.
When on, pressing the mode switch (the left hand button) will cycle through Low, Med, High, Turbo, Low etc.
Pressing and holding the mode switch (when on) for about 1s will enter Strobe mode.
Pressing and holding the mode switch (when on) for about 3s will enter SOS mode.
If either flashing mode is being used, a single press of the mode switch returns the TK75 to a constant output mode.
The last used constant mode is remembered when switching on and off.
The TK75 has a built in automatic downshift from Turbo to High after 21minutes. To return to Turbo press the mode switch again.
Batteries and output:
The TK75 will run on 2 or 4 18650s and operates on 8.4V input voltage. The 4x18650s used for standard operation are used in 2S2P configuration. If using only 2x18650 they are in 2S configuration.
As a last resort, Fenix state the TK75 can use 4 or 8 CR123s, but doing so will force the TK75 into a single output mode.
When using just two 18650s, Turbo does work, but only for about 1-2 minutes before dropping to High.
In this section we will look at the standard configuration of the TK75, but in a special section included after the main review I will cover the TK75 with up to two extended runtime kits fitted powering the TK75 with 12x18650s (in 2S6P configuration)!
In keeping with the ‘Totally Fenix’ ethos of this series of reviews, the TK75 is being powered with Fenix ARB-L2 cells.
To measure actual output, I built an integrating sphere. See here for more detail. The sensor registers visible light only (so Infra-Red and Ultra-Violet will not be measured).
Please note, all quoted lumen figures are from a DIY integrating sphere, and according to ANSI standards. Although every effort is made to give as accurate a result as possible, they should be taken as an estimate only. The results can be used to compare outputs in this review and others I have published.
Fenix TK75 I.S. measured ANSI output Lumens PWM frequency (Hz) Turbo 2722 714Hz and 41.6kHz High 1199 181Hz Medium 464 0 Low 43 0
Strobe has a dual frequency using 6.7Hz and 15.6Hz (8 flashes at each frequency)
As the TK75 utilises an electronic switch, there is parasitic drain to consider. At 58uA this is insignificant and would take over 10years to deplete a set of 4 18650s.
The runtime graph was intended to capture the maximum output capability. This meant having to constantly monitor the test as every 21 minutes it switches down to High and needs to be nudged back up to Turbo. After doing this, the following output trace is the result.
In The Lab
Introduced in Winter 2012 ANSI standards include maximum beam range. This is the distance at which the intensity of light from an emitter falls to 0.25lux (roughly the same as the lux from a full moon). This standard refers only to the peak beam range (a one dimensional quantity), so I am expanding on this and applying the same methodology across the entire width of the beam. From this data it is possible to plot a two-dimensional ‘beam range profile’ diagram which represents the shape of the illuminated area.
In order to accurately capture this information a test rig was constructed which allows a lux meter to be positioned 1m from the lens and a series of readings to be taken at various angles out from the centre line of the beam. As the rig defines a quadrant of a circle with a radius of 1m, all the readings are taken 1m from the lens, so measuring the true spherical light intensity. The rig was designed to minimise its influence on the readings with baffles added to shield the lux meter from possible reflections off the support members.
The distance of 1m was chosen as at this distance 1lux = 1 candela and the maximum beam range is then calculated as the SQRT(Candela/0.25) for each angle of emission.
In this plot, the calculated ANSI beam ranges are plotted as if viewed from above (for some lights there may also be a side view produced) using a CAD package to give the precise 'shape' of the beam.
Starting with the 5m range grid, the TK75’s beam profile totally whitewashes the grid at this range.
Zooming out to the 50m grid, and here the TK75 is shown along with the three other Fenix lights that are part of this series of reviews, and this clearly shows how the TK75’s output totally overwhelms the others.
The indoor beamshot shows the super bright hotspot and wide spill. The spill does exhibit typical flower like shaping round the outer spill due to the compound reflector.
To show the TK75 in context, I am comparing it to the well regarded thrower the TK41. The TK41 itself is an impressive light and has been photographed here at the exact same exposure that has been used for the TK75 photograph which follows.
Now switching on the TK75 and with over three times the output of the TK41 the TK75’s performance is fantastic.
Carrying the TK75
It seemed justifiable to add a section just to look at the considerations of carrying the TK75, as unfortunately it does not come with a belt holster.
After approaching Fenix about this, I was told that the TK75 is not considered suitable for belt carry so there is no holster, nor will there be one made available.
It is not an easily ‘pocket-able’ light, well I’ve temporarily put it in the leg pocket on my cargo trousers, but you can’t really walk along with it like this.
So, what are the options? As supplied, the TK75 only has a wrist lanyard. Considering that Fenix consider the TK75 is too big to belt carry, then what about a shoulder strap? Again this is not available, so you might have to rig something up yourself.
Thanks to Martin at Torch Direct, I have been using a holster that fits the TK75.
This is actually a JETBeam RRT3 holster, but if one of the two straps is wrapped behind the holster, the Velcro strap will hold the TK75 securely.
Another less tidy alternative is a MOLLE utility/water bottle pouch or similar, such as the one I’ve got mounted on a rucksack here.
Test sample holster provided by Torch Direct for this review.
The Extended Runtime Kits
The TK75 in its standard form certainly stands tall amongst its peers, but it has one excellent feature which is unique in its class. Fenix have cleverly designed it to be expandable with battery holders that can be stacked and work in parallel. This is available in the form of the AER-TK75 Extended Runtime Kit.
As the extended runtime kits operate in parallel, working voltage is not increased, instead capacity is increased. The crucial factor here is that in using at least one extended runtime kit, the load on individual cells is significantly reduced and this allows the cells to operate more efficiently and to deliver more energy.
It is widely demonstrated that the higher the current draw from a cell, the lower the overall mAh that can be delivered, so instead of simply having a spare set of 18650s in your pocket, will preloading them in an extension kit provide real benefits in terms of overall runtime? The answer is yes, and the tests results confirm this.
For this special Extended Runtime Review section, Fenix’s maximum recommended configuration has been used. Fenix advise that only a total of three sets of batteries be used which equates to the TK75 plus 2 Extended Runtime Kits.
As this review is keeping the sample light ‘Totally Fenix’ an additional 8 ARB-L2 cells are being used.
Each of the kits consists of a battery tube extension, a stackable battery holder, and a spare o-ring.
The Extended Runtime Kits laid out.
The full set of cells, battery holders, and battery tube extensions laid out with the TK75.
Starting with the basic TK75.
Adding one Extended Runtime Kit
And then the next, bringing the TK75 up to its maximum size and weight.
So how does this overgrown light handle and how much does it weigh?
Considering there are 12 x 18650 cells now installed in this light, it is very manageable, and the result of the weigh-in is:
TK75 (with 4x18650 fitted) – 713g
TK75 plus 1 extension (with 8x18650 fitted) – 1066g
TK75 plus 2 extensions (with 12x18650 fitted) – 1418g
Three runtime tests were carried out with a matched set of cells for each battery holder to ensure the results reflect the effect of increasing the available capacity evenly as each additional set of batteries was added to the test.
Due to the TK75 automatically stepping the Turbo down to High, each test had to be monitored and the Turbo mode re-instated at each step-down.
These downshifts in output are shown clearly on the runtime graph as the sections of Turbo output.
Here you can see the superimposed runtime traces for the basic TK75 and with one and then two Extended Runtime kits.
Although the advantage of using the extended runtime kits are reasonably clear on the graph, with the overall runtime available being the most obvious gain, looking at the actual runtime logs provides the following figures:
1h02m of Turbo output
62 mins of Turbo per set of 4x18650 cells
TK75 + 1 extension:
2h20m of Turbo output (which is 2.26x the Turbo runtime compared to one set of 4 cells)
70 mins of Turbo per set of 4x18650 cells
TK75 + 2 extensions:
3h37m of Turbo output (which is 3.5x the Turbo runtime compared to one set of 4 cells)
72.3 mins of Turbo per set of 4x18650 cells
So now it becomes clear that using an extra set of cells in an extended runtime kit does not simply double the runtime, but due to the cells having a lower current draw, they are able to deliver more energy and give you a real benefit in overall runtime compared to running one set down and then swapping for the spare set.
Each battery holder can use either 2 or 4 cells, so with the extended runtime kits, you can run as many pairs of cells as you have, always gaining in efficiency the more you use. Even if you only have 6x18650 cells, using them in the 2S3P configuration will give more runtime per cell than if you use 2S2P. Each pair of cells you can add provides an advantage.
Due to the parallel connection of the stacking battery holders, you can also keep the extended runtime kit in place even if only using 4 cells. The empty battery holder simply acts like a dummy cell and provides a connection to the driver circuit.
With the extended runtime kits, the TK75 gives you enormous flexibility in size, weight, and runtime options with a maximum of 3h 37m at over 2700lm!
What it is really like to use…
The TK75 is truly a portable searchlight. The beam is primarily configured for throw and the output is regulated at 2700+lm making this a light for working at long distances. Its size, weight and massive output mean this is not something you would use for the average every-day task.
Where the TK75 comes to life is for large area lighting and long distance searching. It is a handheld light with the performance of 100-150W halogen bulb search lights normally tethered to cumbersome lead-acid 12V battery systems (or your 4x4).
Even when running the TK75 for extended periods on Turbo, it never gets excessively hot. The runtime tests were carried out with a small USB powered fan to provide some cooling and the maximum temperature recorded was 40 °C. The large head and cooling fins work effectively to dissipate the heat. In normal use and with the user’s hand also providing additional heat sinking I’ve not experienced and overheating issues.
As a lighting tool the TK75 excels. Depending on your particular requirements of runtime or size, the TK75 can be adjusted to fit. Whether checking livestock in a field, scanning for quarry (vermin or game), providing security through lighting up your property or just enjoying the incredible range of the beam, the TK75 takes it in its stride.
Test samples provided by Fenix and MyFenix for review.
Thanks go to Rob of MyFenix for helping to make this series of reviews possible.