Fireflies ROT66 gen 2

Fireflies ROT66 II review

Fireflies ROT66 gen2 Specifications

Brand / ModelFireflies ROT66 gen 2
LEDSST20/ Nichia / XPL Hi
Beam intensity40000-100000 cd
Battery config.1-3*18650
MaterialAluminum + stainless
ReflectorTIR optics
WaterproofIPX 8
Review dateNovember 2019


In 2018 we got surprised by Fireflies entering the flashlight market with a very successful flashlight, namely the Fireflies ROT66. It’s a Hi CRI flashlight with an output of 5000 lumens. In 2019 they upgraded their flagship and included even more LEDs, 12 in total. They now also give you a wider choice of emitters, plus some nice extras. All in all, this is going to be an interesting review, especially if we compare it to its older sibling.

What you’ll get:

Upon receiving the Fireflies ROT gen 2, I noticed the exact same packaging from the 1st version. I assume they still had enough of them lying around, but I would have preferred to see a difference in packaging as well. Not saying that the quality is bad, its quality is better than even some premium flashlights. I’m talking about you Fenix… lol. I got some extra accessories as well.

  • Fireflies ROT66 gen 2 flashlight
  • Lanyard
  • Holster
  • Tripod screw
  • O-rings
  • Manual
  • 45 degrees TIR lens
  • Stainless steel tail cap (optional accessory)
  • Light diffusor (optional accessory)

Handling of the light

In comparison to their previous generation, this has rougher knurling. It doesn’t only feel grippier,  it also looks better IMHO. The diameter hasn’t really changed and being a 3*18650 flashlight it feels a bit more comfortable to hold.
Besides these aesthetic and functional improvements, they also changed the side-switch, which now protrudes instead of being flush with the body. It still doesn’t feel very solid though. But, I have to say that this still an improvement over the previous one, and improves functionality! And on top of that, they increased the hole for the lanyard attachment so it now fits a normal tripod mount!

Tail-standing? yup!

Build Quality, knurling, threads, and anodization

FireFlies produces high-quality products, and the ROT66 gen 2 doesn’t disappoint either. The anodization is done well, just like the machining and knurling on the flashlight. There was only 1 thing that didn’t go so well, and that was the O-ring. Somehow it got damaged while unscrewing the body and putting it back on.

With this package, I also received a white diffuser. Interestingly enough, it doesn’t fit the ROT66 gen2. Mistake? The holster doesn’t seem to be made of high quality and is just a nice extra accessory. Very basic. The lanyard seems to be okay.

One thing they improved on is the tailcap. Instead of the extremely lightweight tailcap on the 1st generation, they now have an optional stainless steel endcap. And it’s rather heavy compared to the original tailcap,  45grams (0.55oz) vs the original 15.4 gr (1.58oz).

Compared to the 1st generation

LEDs, Lens, Bezel, and Reflector

I received the Fireflies ROT66 gen2 with 12*XPL-Hi LEDs for maximum brightness and neutral color. My first generation ROT66 has Nichia LEDs which are completely different. It has fewer LEDs and a different color temperature. Therefore most comparisons will fail. The Nichia’s will have a higher CRI, while the Cree XPL have higher output. Mines are 5000K, which is a sweet spot. Not too warm, nor too cool. Since these are XPL Hi’s they don’t have a dome and should increase throw even more unless you use the additional 45 degrees TIR optics.

You can choose from the following emitters:

  • SST20 10W 5000K NW
  • SST20 6500K 10W CW
  • Nichia 219B-V1 R9080
  • SST20 4000K FD2 CRI95
  • SST20 2700K JA3 CRI95
  • XPL Hi V3 3A 5000K Neutral White
  • XPL Hi V3 1A Cool White
  • XPL Hi V2 5A 4000K Neutral White
  • Osram 15W 6500K emitter

The bezel is stainless steel, just like with its predecessor. The Tailcap, however, is replaced with a normal black aluminum tailcap and stainless steel as an optional attachment.

You’ll get a second TIR optic within the package. This is not a spare but a replacement. Meaning that the original TIR optics have a 15 degrees angle of light (more throw) and the additional TIR optics are 45 degrees and therefore more floody. I really like that Fireflies added them as part of the kit! Well done FireFlies! Aux LEDs
These are the colorful LEDs on the LED board for improved appearance but are also functional. They change colors relative to the Voltage of the batteries. You can however also turn them off if you’d like, or dim them.

  • 4.2-3.7V = Deep blue + ice blue + green
  • 3.7-3.3V = Deep blue + ice blue
  • 3.3-3.0V = Red
  • 3.0-2.8V = Aux lights OFF

How to turn off the secondary, AUX Leds on the Fireflies ROT66 gen2 and other Anduril flashlights?

To turn the AUX lights off, do the following:  from the OFF position click the switch 7 times. That’s it.
The next time you click 7 times, the AUX LEDs will be dim.
The next time you click 7 times, the AUX LEDs will be bright again, which is the default setting.


  • Length:  108 mm ( 4.275”)
  • bezel diameter:  50 mm (  1.963”)
  • Body diameter: 46 mm ( 1.82 ”)


  • Empty, original tail cap:  305.6 g (  10.78 oz)
  • Empty, original tail cap:  335.1 g (  11.82 oz)
  • With 3 Sony batteries:  449.4 g (  14.45 oz)

High power flashlights

From left to right: Haikelite MT03 TA, BLF Q8, FireFlies ROT66 gen2, Fireflies ROT66 gen 1, Emisar D18. All of them are high power flashlights!

The second picture shows the 1st generation next to this light.

Driver & User Interface:

The Fireflies ROT66 gen 2 uses a firmware called Anduril. A Budgetlightforum member named Toykeeper wrote the code for the firmware.

By default, the ROT66 II uses a smooth ramping mode.

Check out the full Anduril UI manual here.

Keep in mind that the AUX LEDs are always on by default.

From OFF:

  • Single-click: ON
  • Double click: Turbo
  • 3 clicks: Battery check

Enter Special/Fun modes from OFF:

  • 2 clicks + hold: Strobe modes
  • 4 clicks: Lock Out mode (momentary on: dim)
  • 5 clicks: momentary mode (Bright) ( you can only deactivate by breaking electrical contact between the batteries and the driver by unscrewing the body from the head.
  • 6 clicks: Muggle mode

From ON:

  • Single-click: Off
  • Double click: Turbo
  • 3 clicks: change ramping mode. Instead of a smooth increase, it has 6 little steps between Low and Max.
  • 4 clicks: change to ramping configuration mode
  • Press and hold: brightness ramps up.. release and press and hold again to ramp down.


Read the full manual on how to access and customize these modes. Also, see the firmware picture.

  • Blinky Utility mode:
    • Battery check
    • Sunset Mode
    • Beacon mode
    • Temperature check
  • Strobe / Mood modes:
    • Candle
    • Bike flasher
    • Party strobe
    • Tactical Strobe
    • Lightning mode
  • Lockout mode (can’t use the light) (activate by 4 clicks)
  • Momentary mode (signaling/morse coding)
  • Muggle mode: (safer for children)
  • Configuration mode
  • Ramp config mode

Lock Out Feature:

  • From OFF: 4 clicks. To deactivate click another 4 times.

Protection Features

The ROT66 II has a low-voltage-protection (LVP) and thermal regulation.

LVP makes the light step down to a lower level when the battery is low, and if the light is already at the lowest level, it shuts itself off. This activates at 2.8V. LVP adjustments happen suddenly, in large steps.

Thermal regulation attempts to keep the light from overheating, and otherwise adjusts output to stay as close as possible to the user-configured temperature limit. Thermal adjustments happen gradually, in steps so small they are difficult for humans to perceive.

Batteries and charging:

They got rid of the battery carrier design. Especially for this kind of light, a battery carrier was a little over top. It needs 3 high Amp batteries for it to reach maximum output. Although most multi-cell flashlights use 4 cells, the ROT66 uses only 3. This could be a pro or a con. At least the diameter of the flashlight could be a few millimeters less.

Important: Flat Top, unprotected 18650 batteries won’t fit!


I took all of my readings from fully-charged Sony VCT5A batteries.

Lumen measurements

All output numbers are relative to my home-made Integrating Sphere and which is set up with a Hagner E4-X professional Lux Meter for measurements. For bright flashlights (above 5000 lumens) I am adding a Kenko PRO1D ND-16 filter. The base measurement was done with a Convoy S2+ that was tested at 137 lumens.

According to the FireFlies website, it is supposed to reach 12,000 lumens. I was unable to reach that, but at almost 9,000 lumens it’s definitely a pocket rocket. It is about 1000 lumens brighter than the gen1 with Nichia LEDs.

Tested with Sony VTC5A, and the luxmeter used a camera ND filter.

ModeMeasured Output
16.13 Lm
230 Lm
381 Lm
4218 Lm
5435 Lm
6858 Lm
71,759 Lm
Turbo8,752 Lm


This is a second runtime test. The first one was unreliable. This time I used my integrating sphere to measure the runtime. I used the Extech SDL400 this time and the runtime is completely different from the first runtime test. The average output is about 450 lumens for most of the runtime.

Here is the runtime graph from the first 10 minutes.

Throw measurement:

Measurements were taken indoors with a professional Hagner E4-X Lux Meter. 
Using turbo mode, I get a maximum of:

  • Indoors (5m): 55000 cd =  496 meters / 0.29 miles (exactly the same as FireFlies claimed)
  • Outdoors (10m): 49000cd = 443 meters/  0.28 miles


Beamshots are shot with Canon EOS 5D mk2: ISO1600, F4, 1/4 sec. 50mm, 5000K.

Overall conclusion


  1. A large amount of emitter choice, from Hi CRI to High Output
  2. Secondary AUX LEDs
  3. Nice amount of accessories
  4. Bright
  5. Extra accessories available like SS tailcap and diffuser


  1. UI can be complicated
  2. It eats the O-ring

Overall Rating: 4 stars: ★★★★

Author: Marco

If you are looking for a very bright, but yet pocketable flashlight with great runtime? Have a look at the ROT66 gen 2. It’s not a lot brighter than generation 1, but it is an improvement over the gen1. It’s a little shorter, no battery carrier, more LEDs, and AUX secondary LEDs. The only thing is that it uses 3 batteries instead of the regular 4. For the rest a great performer!

Fireflies ROT66 gen2 for sale

Discontinued. Check out the list with brightest flashlights instead.

1lumen selects and reviews products personally. We may earn affiliate commissions through our links, which help support our testing.