Sofirn SP35 Flashlight Review

The Sofirn SP35 flashlight is now available with advanced temperature regulation (ATR). Read on for testing on this high-output flashlight!

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Official Specs and Features

Here’s a link to the Sofirn SP35 ATR flashlight product page.

Versions

Notably, there are two versions – the ATR version and the older version, which doesn’t have thermal regulation.
As far as bodies, it looks like just the black body option. And finally, emitters – there are two temperatures: 5000K and 6500K (seen here).

Price

The complete package on Amazon is $40. That includes the 21700 cell, which makes it a complete package. Now, I wouldn’t pick 6500K, but that’s what Amazon has, and so this seems like a pretty solid deal. Here’s an Amazon referral link.

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Short Review

The Sofirn SP35 ATR flashlight is a pretty cool light. The 6-step modes are great – low is low and high is high, and there’s plenty between. If you don’t like stepping, there’s ramping too!! The price is great!

Long Review

The Big Table

Sofirn SP35 (ATR) Flashlight
Emitter:	Luminus SST-40 (6000-6500K)
Price in USD at publication time:	$31.99
Cell:	1×21700
Turbo Runtime Graph	High Runtime Graph
LVP?	Switch warning, then off.
Switch Type:	E-Switch
Quiescent Current (mA):	0.02
On-Board Charging?	Yes
Charge Port Type:	USB-C
Charge Graph
Power off Charge Port	With cell: All modes Without cell: Lowest 4 modes
Claimed Lumens (lm)	2000
Measured Lumens (at 30s)	1633 (81.7% of claim)^
Candela per Lumen	14.6
Claimed Throw (m)	332
Candela (Calculated) in cd (at 30s)	1069lux @ 4.81m = 24732cd
Throw (Calculated) (m)	314.5 (94.7% of claim)^
All my Sofirn reviews!

^ Measurement disclaimer: Testing flashlights is my hobby. I use hobbyist-level equipment for testing, including some I made myself. Try not to get buried in the details of manufacturer specifications versus measurements recorded here; A certain amount of difference (say, 10 or 15%) is perfectly reasonable.

What’s Included

• Sofirn SP35 ATR flashlight
• Sofirn 5000mAh 21700
• Charge cable (USB to USB-C)
• Lanyard
• Spare o-rings (2)
• Manual

Package and Manual

Build Quality and Disassembly

For $40, this Sofirn SP35 ATR flashlight has superb build quality. Really, even for more money, this would be a reasonable light. Nothing is notably bad regarding the build. In fact, there are many things to really like here!

Here on the head are some cooling fins. They’re not incredibly deep, but you wouldn’t expect them to be on a tube light.

The tailcap is surprisingly bare – this light seems to want to be a dual switch light, but there’s just the e-switch. I like it very much in this setup, though.

Both the head and tail come off the cell tube.

Threads here are great, too – square-cut, anodized, and well-lubed. They’re quite long.

The head end has the same threads.

A very thick beefy spring graces the tailcap, and the whole piece is held in by a retaining ring.

No spring is on the head end, just some brass contact rings.

As I said above, the threads are the same on both ends. This means the cell tube is reversible – you’ll see later why that’s good.

Size and Comps

Dimension: 126mm (length) × 28mm (head diameter)
Weight: 73 grams (without battery)

If the flashlight will headstand, I’ll try to show it here. If the flashlight will tailstand, I usually show that here, too.

Here’s the test light with the venerable Convoy S2+. Mine is a custom “baked” edition Nichia 219b triple. A very nice 18650 light!

And here’s the light beside my custom-engraved TorchLAB BOSS 35, an 18350 light. I reviewed the aluminum version of that light in both 35 and 70 formats.

Retention and Carry

A lanyard is included and attaches through a hole in the tailcap, as seen below.



Only one side has the lanyard hole. It’s just one hole, too, and so when tailstanding, the lanyard will get in the way just a little bit. It’s very thin, though, so that’s not the biggest problem.

A pocket clip is included, too.

This clip is designed to attach in only one place on the cell tube. By default, that is on the tail end, but since the cell tube is reversible, you can set the light up as a “bezel up” carry if you wish.

It’s a “pretty deep” carry clip, especially with the overall size of the light.

Clip hug!!

There’s no pouch, magnet, or anything else.

Power and Runtime

The Sofirn SP35 ATR flashlight is a single lithium-ion cell light. The cell tube is 21700-sized, and that’s the cell that ships in the package.

This is a flat top unprotected 21700. Other type 21700 cells should work with no issues in the Sofirn SP35 ATR flashlight.

The cell is installed into the Sofirn SP35 ATR flashlight in the usual way – positive end toward the head.

Below you can see a few runtime tests. The ATR feature – Advanced Temperature Regulation – of the Sofirn SP35 ATR flashlight can be readily seen after the initial stepdown. The output is extremely active in managing the temperature around 40 degrees Celsius. The setting isn’t something that can be changed. (Being able to change this to 50°C or so would be great!)

It really seems that Turbo is the only mode that requires ATR – temperature on High, and lower never really gets unmanageable at all.


In all tests, the Sofirn SP35 ATR flashlight turns off after a switch warning.

Charging

Built into the Sofirn SP35 ATR flashlight is USB-C charging. This is a nice “current generation” charging method (better than micro-USB).

The charge port is in the head, just opposite the switch. These two items (switch and charge port cover) are different enough that you’ll not confuse them.

Sofirn includes a charge cable – USB to USB-C. It’s a surprisingly high-quality cable. I tested operation with USB-C to USB-C, and that works (but looks to just be at 5V). Still, it works, which is good.

Here’s a charge graph – I logged only with USB to USB-C, since that’s the cable Sofirn supplies. Charging is very good – around 2A at a peak, and fills the cell to around 4.15V. When topped off in a bay charger, the cell took only around 50-60mA more (ie, practically negligible).

While charging, the indicating switch will be flashing red. When charging is complete, the switch will turn green.

Modes and Currents

Mode	Mode Claimed Output (lm)	Claimed Runtime	Measured Lumens	Tailcap Amps
Turbo	2000	1h53m	1633	4.83
High	950	3h40m	803	1.73
Medium	400	5h35m	349	0.57
Low	120	17h36m	107	0.16
Eco	7	160h	10	0.01
Moon	1	31d	1	3.85mA

Pulse Width Modulation

There’s no PWM on any mode. There’s a little sawtooth on one mode, but this isn’t visible.

Here you can see a “baseline” – a chart with almost no light hitting the sensor.
Then there’s the Ultrafire WF-602C flashlight, which has some of the worst PWM I’ve seen. It’s so bad that I used a post about it to explain PWM! Here are multiple timescales (10ms, 5ms, 2ms, 1ms, 0.5ms, 0.2ms) to make comparing this “worst” PWM light to the test light easier. That post also explains why I didn’t test the WF-602C at the usual 50us scale.

User Interface and Operation

The Sofirn SP35 ATR flashlight is controlled by a single switch. It’s an e-switch on the side of the head.

This switch also has indicating features – below it’s seen indicating red for low voltage. Notably, the switch will indicate for 5 seconds after the light is turned on, as follows:

Green: remaining battery power is good
Red: remaining battery power is poor (less than 30%)
Red Flashing: recharge or swap cell immediately.

There’s a surprising amount of travel on this switch. It’s also quite proud

Here’s a user interface table!

State	Action	Result
Off	Click	On (Mode Memory)
Off	Hold	Moon
On	Hold	Group 1: Mode cycle (Eco, Low, Medium, High only) Group 2: Ramp up
Any (except Turbo)	Double Click	Turbo
Turbo or Strobe	Click	Previous state
On	Click	Off
Turbo	Double Click	Moonlight
On	Click 4x	Switch between Group 1 and Group 2
Any	Click 3x	Strobe
Strobe	Double Click	Strobe advance (Strobe, Beacon, SOS)
Off	Click 4x	Lockout
Lockout	Click 4x	Unlock
Lockout	Click	Main emitter blink 2x to indicate lockout
Lockout	Hold	Momentary Moonlight

Why you’d want to double-click from Turbo to get to Moonlight, I have no idea.
Group 2 (Ramping) is very similar to the above Group 1, except that holding the switch will cause the light to ramp up. Loosening then holding the switch again within 1.5s will cause the ramp to switch directions. So it’s possible to ramp up or down. Double-click still gets Turbo.

LED and Beam

In my review copy of the Sofirn SP35 ATR flashlight is a Luminus SST-40 emitter in 6500K. This emitter is surrounded by a smooth and quite deep reflector.

The bezel has some shape, so when headstanding, some light can escape.

Check out the smooth reflector!


Maybe mine’s 6500K, but I have to say it’s still a clean beam and doesn’t feel so much like 6500K. Warmer than 6500K.

Beamshots

These beamshots always have the following settings: f8, ISO100, 0.3s shutter, and manual 5000K exposure. These photos are taken at floor level, and the beam hits the ceiling around 9 feet away.

Tint vs BLF-348 (KillzoneFlashlights.com 219b version) (affiliate link)

I keep the test flashlight on the left and the BLF-348 reference flashlight on the right.

I compare everything to the KillzoneFlashlights.com 219b BLF-348 because it’s inexpensive and has the best tint!

Conclusion

What I like

• Great deal at $40.
• Good beam profile
• Throw is good
• Ramping option if you want it…
• But the stepped group is very smart too
• USB-C charging works great
• No PWM

What I don’t like

• 6500K
• I wish the switch was just a little lower to the body – it sits a bit too proud
• Ramping is a little bit awkward with ramp speeds

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Notes

• This light was provided by Sofirn for review. I was not paid to write this review.
• This content originally appeared at zeroair.org. Please visit there for the best experience!
• Please use my Amazon.com referral link to help support zeroair.org!