[Review] Sofirn SP35 - SST40 21700 Buck Driver

LED Flashlights – General Info 21700 Flashlights
1

Sofirn SP35 Review

Here’s the rundown from Sofirn:

* Luminus SST40 6000K - 6500K

* Operating voltage: 3.0V – 4.2V

* Driver: Constant current buck driver

* Battery options: 1x 21700 rechargeable lithium-ion battery

* Dimension: 126mm (length) × 28mm (head diameter)

* Weight: 73 grams (without battery)

* Flashlight body: Aerospace grade 6061 grade aluminum alloy, hard-anodized to military grade specification type III

* Toughened mineral glass lens

* Water resistance i.a.w. IPX-8 (up to 2 meter under water, not for diving)

* Mode Memory: memorizes the last brightness level used in the general modes (Eco/Low/Med/High)

* Wrong polarity protection from improper battery installation

* Low voltage warning: yes

* Low voltage protection: yes

* Advanced Temperature Regulation (ATR) technology


What’s inside the box:

* Sofirn SP35

* 4000 mAh 21700 battery

* Reversible pocket clip

* USB-A to USB-C charging cable

* Lanyard

* User manual

* Spare o-rings

Operation details:

* Choice of stepped (default) or ramped modes (4x click from On)

* Shortcut to Moon from Off (hold)

* Shortcut to Turbo from Off or On (2x click)

* Lockout with momentary Moon (4x click from Off)

* Battery indicator LED in the switch

Other info/observations:

* Nicely regulated buck driver

* USB-PD (USB-C to USB-C) compatible

* Charging rate of 2A (spec, I observed 1.8A)

* Charging termination: 4.15V

* Low voltage cutoff: 2.90V

* This is from the initial batch where ATR is not enabled

Runtime & Measurements

  • In Turbo mode, it’s way too hot after 5 minutes
  • In High mode, it hovered around 54°C
  • Using a maukka calibrated lumen tube…
  • Turbo spec is 2000 lumens, I saw 1740 lumens at 0 seconds and 1677 at 30 seconds
  • High spec is 950 lumens for 3 hours and 40 minutes, I saw 840 lumens for 2 hours and 16 minutes
  • Medium lumens: 357 (spec: 400)
  • Low lumens: 114 (spec: 120)
  • Eco lumens: 14 (spec: 7)
  • Moon lumens: 0.4 (spec: 1)
  • Throw spec: 27,520 cd for 332 meters
  • Throw measured: 24,250 cd for 311 meters (pretty close to spec)





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My favorite Sofirn Light so far, outside of the AAA lights!

The UI is nice, I really like it and I knew the low was higher than the acclaimed 7 lumens! The Low to Medium jump is not as jarring as the numbers would seem, like the Thrunite Ti3 medium to high.

Great review, thanks!

3

Why the fluctuation in the temperature graph if yours has no ATR?

4

Just some “jitter” in the IR temp sensor reading. Those variations are like a couple tenths of a degree.

5

Thanks . I ask because ATR graphs look similar and fluctuations have been seen with the naked eye. I am considering this light or the SP33v3 but both seem to have this condition. What is the light on the right in your photo?

6

The light on the right is the SP31 V2.0 - it’s extra-tall to accommodate a forward-clicky tailswitch.

After seeing the wildly fluctuating ATR on the SP33 V3, I’m thinking maybe I should get the SP35 before they manufacture a batch with ATR.
I was planning to buy the SP35 after they added ATR, but perhaps it’s better to have no ATR than potentially quirky ATR…

7

I politely disagree. See how stable the lumen output is? Super flat? You only get that with a well regulated buck, boost, or buck-boost driver. The ATR fluctuations on the SP33v3 and the HD20 are much much different.

8

Damn, that’s nice regulation in the ’35!

9

Didn’t Sofirn already have an SP35 back in ’17? Something similar to the SF14 but with 3 x 18650 cells.
Lexel had done a review here

And thanks for the heads-up GC. Finally, a light to warm up my winter blues!

10

Ohhh, that makes my head hurt. Was thinking a typo of a ’36 (3×18650), but nope, actually etched with “SP35” on it, and this also SP35 is 1×21700. Ow, ow, ow…

11

Hah, I found that too when I was looking online for info about this light.
Of all the model numbers Sofirn could choose, they decided to reuse one…

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When the ATR model arrives, think it will be any better?

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I don’t know if anyone knows at this point. In the discussion thread it says “improved ATR technology” so it sounds like they know it needs work. We just don’t know how good their improvements are yet.

14

Fingers crossed. I know the SD05’s ATR looks OK to the eye anyway, never saw a graph of it though. This SP35 is real nice. Good review.

15

At least in the SD05 I tested it was a boost driver and no ATR. After the timed step-down, nice flat output.

16

Why would you think ATR would make the light better?
As seen from gchart’s graphs, the regulation is very steady and no bouncing about.

I for one jumped on ordering a unit before Sofirn makes another ‘Frankenstein’.*

As I work with these lights, it’s quite disturbing to have them gradually drop and after a few minutes, I’m trying to figure why there’s no illumination when there was. My eyesight may be falling, but not to the point of tunnelling!

  • I suspect they had a problem integrating their standard ATR with the buck driver. Someone will eventually purchase an AE light (which does have a newer ATR version) and make some analysis.

edit: Today it’s –20ºC outside. Damn if I care about overheating!

17

Good to know it has a properly implemented port and will charge via a C2C cable.

I like the regulation, and can even live without the ATR (whose performance may be questionable), but the beam shot in another review reminded me of a Mag Lite, and not in a good way.

With all the little issues, and lack of a 5000k option, I’m debating whether it’s better just to wait for the inevitable v2 version.

18

Same here, I’d love it if this light would come in 5000k (or maybe even 4000k but probably not, that seems to be my sweet spot though) and with Anduril… Maybe some day!

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My thoughts:

  • With the ATR, I think it’s only necessary if you plan on keeping your light on Turbo for extended periods and want to make sure you don’t get burnt. Otherwise, I think this no-ATR batch is great.
  • I understand the CCT preference. 6000K isn’t exactly my favorite. I may eventually try to swap it out.
  • As for the beam, like I said… I’m either not sensitive to it or mine has the newer reflector. Here’s a couple beamshots on my white ceiling.

Note: if there is any coloration in the beam, take it with a grain of salt. I’m colorblind and can’t confirm if the tint matches reality.

Beamshot 1: ~18 inches away (~46cm) using Low mode, ISO 80, 1/200 second exposure, 6000K white balance

Beamshot 2: ~8 feet away (~244cm) using Low mode, ISO 80, 1/50 second exposure, 5000K white balance

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ATR is fine in my book if it doesn’t throttle down too soon. My wife picks up a light to go to the garden or lend one to someone, etc. Turbo could burn down my house with some lights. It has to be done well though. It’s like a gun without a safety which I do own but they have to be treated with special care.