Fireflies ROT66 review (3x18650, 9x219B)

Excellent review once again! Think I do have a potential fix, can't be sure but potentially. I'll be talking to them today.

Still wondering about the lumens. In theory this light should be equal to 3 triples, 1 batt per 3 LED's. I don't know how the path from the LED's through the battery is, ex: thickness of LED wires, etc., quality of springs, but if an equally tested 219B triple could be tested for comparison, it would be nice to know.

3860 lumens means 429 lumens per LED, or 1287 lumens for a FET based triple.

I only happen to have an Astrolux S41S with 219B sw40k R9080 and MTN17ddm FET driver with bypass on the driver and double springs in the tailcap. It only does 900 lumens max (at 0 sec) with a fully charged 30Q.

edit: another point of comparison is a triple 219C R9050 BLF X6 with a FET (h17f driver), it does 1620 lumens at 0 sec, 1560 lm at 30s.

That's interesting, not the same LED's but big difference per LED.

Thanks Maukka, great review as always.

At 65 degrees, is it still possible to hold the flashlight?

Found another 219B triple, edited my previous comment.

edit: and realized it is actually a 219C CRI90 triple…

Nice review, thanks! :smiley:

65°C was at the head, it takes time to travel to the rest of the body. 65°C is too hot to hold, about 50°C is what I can handle for a short while.

Thanks Maukka

Fireflies mentioned larger domed LEDs like LH351D would not fit. Is this true?

What a review, great

Thanks for this great review, maukka :+1:


Just wondering why my ROT66 could stabilize at ~700 lumens with a temperature of ~43°C (at the head) after hours of testing. I tested it under a 25°C room environment. One possible reason I can think of is, whether the runtime curves are measured directly with a integrating sphere or not. With the sphere attached, the light can heat up noticeably more quickly, so I used to measure this with simple ceiling bounce (and then apply an appropriate multiplier based on the integration result, of course). I may test again once my replacement ROT66 come back to me.

In the runtime test the head isn’t in a completely enclosed space, but I’ll check the temperature at 700 lumens with the light tail standing, thanks for the observation.

Can’t match your results even with a better environment for the convection to take place and without the initial turbo heat buildup.

At 26°C room temp on the 7x7135 mode the head heats up to
45°C at 15 min
46°C at 20 min
49°C at 25 min
50°C at 30 min
52°C at 35 min
53°C at 40 min

It will probably still be handholdable indefinitely taking into account the heat sinking from the hand. Especially outside. So that’s a great choice for the number of 7135 regulators in the 219B model by Fireflies.

Interesting. Sorry that I forgot to mention: I measured the max temperature around the side switch, not the SS bezel. This is because the hottest part I may touch is simply around the switch. I’ll confirm that again once mine is back.

Me too, you can’t measure the temperature from SS with an IR meter anyways. The laser pointer just offsets upwards since the meter is so close.

Yes. I was using an IR meter too.

The wait for mine to come in is excruciating! Thanks for measuring the effect the lens has on the color output. The 700 lumen mode looks super ideal to me for its ruler flat regulated output and amount of pink to its tint.

This thing will be the perfect hiking light.

Are the optics used in the ROT66 the same or very similar as the MF01? How does the lux vs angle graph compare between the two?

I haven’t measured the beam profile for the MF01. It has more even beam, while on the ROT66 the lux fades more gradually towards the wider spill. There’s more of a tunnel vision effect with the MF01, much like on an Olight with XM-L2 and optic.

Here’s a white balance and light level corrected comparison for the two.

Superb review and discussion here,thank you.

This animated GIF is quite mesmerizing…if you concentrate and keep focused on the centre of the spot it looks like blast waves every time it switches between MF01 and ROT66. :nerd_face: