[Review] Sofirn SP35 - SST40 21700 Buck Driver

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gchart
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[Review] Sofirn SP35 - SST40 21700 Buck Driver

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: 1× 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)






Edited by: gchart on 01/19/2021 - 13:53
ReManG
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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!

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

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

pennzy
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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?

Serlite
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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

gchart
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pennzy wrote:
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?

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.

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

09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

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

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

Lightbringer
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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…

09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

Serlite
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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…

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

gchart
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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.

pennzy
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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.

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

Sidney Stratton
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pennzy wrote:
When the ATR model arrives, think it will be any better?

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!

TheIntruder
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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.

Fescron
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TheIntruder wrote:
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.

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!

gchart
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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

pennzy
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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.

gchart
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Ok, and now for the modding crowd out there:

  • After running the light on turbo for a few minutes, the glue was easy to break loose. Using channel-locks and leather gloves for protection and it came open without any damage. I might not have even needed the channel-locks, it opened so easy after running on turbo.
  • Reflector is screwed in
  • The LED is on a copper 16mm MCPCB
  • Centering gasket is 1.15mm thick
  • Including threads, the reflector outer diameter is 25.8mm
  • The business-end of the reflector reduces in diameter after the threads a bit. Where it’s seated in the bezel (the top 2.5mm or so of the reflector), the diameter is 24.0 mm.
  • Reflector height: 16.0mm
  • Reflector (LED) opening: 7.2mm

This thing may end up with a 5000K LH351D or maybe a 3V XHP50.2 or something like that Big Smile



Fescron
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How easy is it to get to the driver-PCB/microcontroller? Perhaps Anduril can be flashed onto it? This seems like a very interesting light for me to do a first mod on. LH351D 4000k 90CRI (with Anduril?) in a 21700 package with type C charging and CC regulation would be pretty awesome!

gchart
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I haven’t removed the driver. Like most Sofirn’s, it’s held in with a little glue but could be tapped out through the holes for the LED wires. On the couple Sofirns with buck drivers that I have dissembled (I’m thinking SP31 V2.0, maybe others) they used a 10-pin PIC-style chip. If that’s true with the SP35, there’s nothing that swaps in very easily. I dunno if I’ll be ripping the driver out of this one – too many irons in the fire right now.

EasyB
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Nice review, thanks. It’s sort of refreshing to see a light without thermal stepdown.

It looks like a nice performing light. And with the low Vf of the SST40 the regulation should be decent in the turbo mode. Did you measure the cell current?

Fescron
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gchart wrote:
I haven’t removed the driver. Like most Sofirn’s, it’s held in with a little glue but could be tapped out through the holes for the LED wires. On the couple Sofirns with buck drivers that I have dissembled (I’m thinking SP31 V2.0, maybe others) they used a 10-pin PIC-style chip. If that’s true with the SP35, there’s nothing that swaps in very easily. I dunno if I’ll be ripping the driver out of this one – too many irons in the fire right now.

Yeah the UI is fine as-is for me I suppose, the only thing I’ll miss is battery voltage readout. Is the SST40 voltage and current wise compatible with the LH351D? And how about the beam profile? Is the reflector fine for both so it could be as simple as a drop-in replacement? If so, I guess I’ll pick up one soon with some LH351D LED’s from sofirnlight.com Big Smile

Lastly, is the LED-carrier board glued down as well with some sort of thermal glue or can it easily be removed you think?

gchart
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EasyB wrote:
Did you measure the cell current?

Just tested it. With the battery fresh off the charger at 4.20 volts, it was pull 4.75 amps (and creeping up) using a clamp meter and short, heavy wire. And that’s when I noticed my shirt was starting to smoke. Oops, you’d think I’d have learned that lesson by now, right?
Fescron wrote:
Is the SST40 voltage and current wise compatible with the LH351D? And how about the beam profile? Is the reflector fine for both so it could be as simple as a drop-in replacement?

The SST40 has a lower vF so the LH351D won’t be as bright or efficient. But if you’d prefer a warmer CCT and higher CRI, it might be a worthy swap for you. If you just want a warmer CCT and don’t care about CRI, grab a 5000K SST40. The SST40 is a 5050 footprint, while the LH351D is a 3535 footprint, so you might want a different centering gasket; not required but probably preferred. The LH351D beam would probably look just fine, both of these are fairly floody LEDs.

Fescron wrote:
Lastly, is the LED-carrier board glued down as well with some sort of thermal glue or can it easily be removed you think?

No thermal glue, just the usual white thermal paste.
Fescron
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gchart wrote:
Fescron wrote:
Is the SST40 voltage and current wise compatible with the LH351D? And how about the beam profile? Is the reflector fine for both so it could be as simple as a drop-in replacement?

The SST40 has a lower vF so the LH351D won’t be as bright or efficient. But if you’d prefer a warmer CCT and higher CRI, it might be a worthy swap for you. If you just want a warmer CCT and don’t care about CRI, grab a 5000K SST40. The SST40 is a 5050 footprint, while the LH351D is a 3535 footprint, so you might want a different centering gasket; not required but probably preferred. The LH351D beam would probably look just fine, both of these are fairly floody LEDs.

Fescron wrote:
Lastly, is the LED-carrier board glued down as well with some sort of thermal glue or can it easily be removed you think?
No thermal glue, just the usual white thermal paste.

Thank you so much for the info! 4000k LH351D 90 CRI would be ideal for me… Sounds like I’ll get myself a SP35 with some other components in a few days LOL

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gchart wrote:



So the ED’s PCB is held in place by the reflector pushing it down?
gchart
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Yes. That screw keeps it from spinning. Pressure from the reflector holds it down. This is very common: many Sofirn’s, Convoy’s, etc all employ this design.

id30209
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gchart wrote:
Ok, and now for the modding crowd out there: * After running the light on turbo for a few minutes, the glue was easy to break loose. Using channel-locks and leather gloves for protection and it came open without any damage. I might not have even needed the channel-locks, it opened so easy after running on turbo. * Reflector is screwed in * The LED is on a copper 16mm MCPCB * Centering gasket is 1.15mm thick * Including threads, the reflector outer diameter is 25.8mm * The business-end of the reflector reduces in diameter after the threads a bit. Where it's seated in the bezel (the top 2.5mm or so of the reflector), the diameter is 24.0 mm. * Reflector height: 16.0mm * Reflector (LED) opening: 7.2mm This thing may end up with a 5000K LH351D or maybe a 3V XHP50.2 or something like that Big Smile


Thx for measurements.

Now i need to find OP refelector...

 

WTB Titanium 4sevens 2xAA tube

TheIntruder
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gchart wrote:

  • 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
!{width:600px;max-width:100%;}http://www.ghart.com/blf/sofirn_sp35/beamshot2.jpg!

That looks much better than this one, from this review.

I like Sofirn, and have a few of their lights, but TBH these kinds of things are frustrating, and can be avoided. If the light isn’t done, then don’t start to produce and then ship them, instead of laying traps for customers who have to wonder whether their will unit fall within the batch with the bad reflector, the buggy driver, or whatever.

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