Review: Fenix TK25 R&B, an 18650 flashlight with high-output red and blue secondary emitters

This TK25 R&B was provided by Fenix for review.

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Quick Review

A request I see on occasion is a light with both white and colored emitters. There are a few options on the market, though many have only low-powered colored emitters, or a single color in a high-powered emitter. The TK25 R&B is a 1x18650/2xCR123 answer to this request from Fenix. It has high-power Cree XP-E2 emitters in both red and blue. Fenix tells me the TK25 R&B is marketed toward hunters, and indeed, I've seen a few people ask for red light to avoid spooking animals and blue light for following blood trails.

Advertised white output is a fairly average 1000 lumens and 225m FL1 throw. My estimates came in a bit higher, but what's really interesting is that output on the highest mode is stable for a while; most similar lights start losing output immediately on the highest mode and show considerable variation in output with different batteries. The light has excellent efficiency at 96lm/w on max. Both red and blue are very bright in practice, and much more effective than their respective 150 and 60 lumen ratings would suggest. In a new direction for Fenix, the TK25 R&B has no timed stepdowns. Instead, there's a thermal sensor, which is fairly generous about how warm the light is allowed to get. It never gets to a dangerous level, but it can become uncomfortable to grip tightly with bare hands. The manual claims the target temperature is 65C, which seems about right.

Operation is similar to some other Fenix dual-tailswitch lights with the main switch being a forward-clicky with half-press for momentary and full-press to lock on. The mode switch cycles through four brightness levels in a low to high order when on and activates a momentary strobe from off. A long-press of the mode switch when the light is on also activates strobe. The last-used steady mode is memorized. The tint is unapologetically cool white, but lacks any notable off-colors. Rotating the head a quarter turn in either direction puts the TK25 R&B in color mode. There is no memory in color mode; high-red is always first. The mode order is high-red, low-red, blue. The mode switch, from off also triggers high-red momentarily. High-red is very bright, and I wish there was a way to start in low-red, as red is often used to preserve night-vision or avoid attracting attention, and high-red won't do either.

Both buttons are fairly proud, and I found myself accidentally starting the light in strobe by pressing the mode switch just before the power switch on more than one occasion. There is no reliable way to lock out activation with a battery installed, and the light lacks low-voltage protection. The manual recommends Fenix brand protected 18650s.

For those who want powerful red, white and blue lights in the same light, the TK25 R&B is one of the few options on the market. The build quality and driver efficiency are excellent, and the light performs better than advertised. There won't be any surprises other than occasionally activating strobe by accident - an artifact, I think of this light's relation to the TK25 IR, a light with infrared secondary emitters marketed for tactical use. I do wish Fenix had chosen neutral white emitters for this light, as the vast majority expressing an opinion prefer neutral white, and Fenix does promote its more accurate color rendering as a benefit on other models.

    • Powerful red and blue secondary emitters
    • Operation is easy to understand without instructions
    • Excellent efficiency on white
    • Stable output for several minutes on maximum mode without a boost driver
    • Solid build quality, typical of Fenix products
    • Excellent waterproofing, even when rotating the head under water
    • No timed stepdownws
    • Cool white only
    • None of the modes are low enough to preserve night-vision
    • Color modes always start on red-high, which is too bright for many of the applications red is used for
    • No low-voltage protection
    • No lockout
    • Easy to activate strobe by accident

Details and technical analysis


The TK25 R&B includes a holster, lanyard, pocket clip, spare o-rings and a user manual. The holster has a velcro belt loop that can be attached to MOLLE gear and a velcro adjustable retention strap.

Modes and user interface

For white:

State Action Result
Off Half-press power switch Momentary (mode memory)
Off Full-press power switch On (mode memory)
Off Mode switch Momentary strobe
Off Mode switch, then power switch at the same time Strobe
On Power switch Off
On Mode switch Next mode (L -> H)
On Long-press mode switch Strobe
Strobe Mode switch Last-used steady mode

For color, selected by rotating the head either direction:

State Action Result
Off Half-press power switch Momentary (red-high)
Off Full-press power switch Red-high
Off Mode switch Momentary (red-high)
On Power switch Off
On Mode switch Next mode (red-high, red-low, blue)

Output and runtime

All tests were performed with an LG HG2 high-drain 3000 mAh 18650 battery unless otherwise noted. Advertised runtimes are with a Fenix 3500 mAh 18650 battery.

Mode | Advertised Lumens | Estimated Lumens | FL1 throw | Graph | Advertised Runtime| Time to 80% | Time to 50% | Time to 10% | Tailcap current ---|---|---|---|---|---|---|---|--- Low | 15 | 15 | 31m | - | 110h | 88h (calculated) | - | - | 34mA Medium | 100 | 117 | 85m | - | 22.3h | 16h (calculated) | - | - | 190mA High | 300 | 353 | 172m | graph | 320 min | 225 min | 225 min | 234 min | 617mA Turbo | 1000 | 1172 | 278m | graph | 120 min | 28 min | 58 min | 80 min | - Red-high | 150 | - | - | graph | 7.5h | 233 min | 233 min | 233 min | 820mA Red-low | 25 | - | - | - | 110h | 39h (calculated) | - | - | 76mA Blue | 60 | - | - | graph | 6.6h | 220 min | 242 min | 253 min | 671mA

Oddly, the low-voltage stepdown in the blue mode is red-low. This light really seems to want to be red.

Time to 10% with a Fenix 3500 mAh battery was 113 minutes, very close to advertised. Uncooled runtime shows some throttling around 12 minutes, but output remains high with nearly an hour to 50%.

The light discharged an unprotected laptop pull below 2.5V, and while clearly capable of reducing output in response to low voltage, does not shut off. There appears to be no standby drain.


The TK25 is comfortable in the hand and lightweight for its size, perhaps in part due to its plastic reflector. Both buttons are very proud and easy to press even with gloves on, though the lanyard loop can get in the way on occasion. Rotating the head is possible one-handed, but easier with two. Four emitters and a rotating head/reflector system do take up some space, and the head is bulky for a light with modest throw. It's better not to use the pocket clip and carry this light in a holster or jacket pocket.

Modification potential

I've decided to start including modifications in reviews. Some people just can't leave well enough alone, and I'm one of them.

With four emitters, two of them cool white, modifying the TK25 R&B was too big a temptation to pass up. Even better, with such stable output from a buck driver even given high-forward-voltage XP-G2 emitters, there's a significant improvement possible. People who read my posts probably know what's coming.

The bezel is glued in place. I had to dunk it in hot water before twisting quite hard with a strap wrench. There are o-rings on both sides of the lens, providing excellent waterproofing. The reflector is plastic. The MCPCB is copper, and the application of thermal paste was respectable.

All the emitters are XP/219 profile, though red emitters have very low forward voltage, and I'm not sure how the driver would respond to something else in their place. XP-Es come in many colors, so there are a lot of potential options for substitution. No colors came to mind that I'd have more use for than red and blue though, so they stayed. The cool white XP-G2s did not.

5000K, 80 CRI Nichia 219Cs are beautiful on a white wall, and awesome outdoors. Output was reduced by about 15% to 1024 lumens, and throw to 224m. Output doesn't tell the whole story though, and this graph makes it clear why this is the right emitter for the TK25 series: 41 minutes to 80% starting from over 1000 lumens without a boost driver on one 18650. I've never seen that before. It's 56 minutes to 50% and 69 minutes to 10%.

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