Sofirn SP35 Flashlight Review

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!

Official Specs and Features

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


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).


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.

Short Review

The Sofirn SP35 ATR flashlight is a pretty cool light.  The 6 stepped modes are great – low is low and high is high, and there’s plenty between.  If you don’t like stepped, 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:  I am an amateur flashlight reviewer.  I don’t have $10,000 or even $1,000 worth of testing equipment.  I test output and such in PVC tubes!!  Please consider claims within 10% of what I measure to be perfectly reasonable (accurate, even).

What’s Included

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

feature photo

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

Here’s the top-down view.  Maybe I’m getting better at this….

top down views top down views top down views top down views top down views

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.

cooling fins

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.

head and tail off

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

tailcap threads

The head end has the same threads.

head threads

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

tailcap spring

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

head and tail contacts

Like 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.

reversible cell tube

Size and Comps

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

If the flashlight will headstand, I’ll show it here (usually the third photo).  If the flashlight will tailstand, I’ll show that here, too (usually the fourth photo).

in hand

Here’s the test light with the venerable Convoy S2+.  Mine’s 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.

beside torchlab boss 35

This is just a fun joke photo – cell tube is gone, with the head atop the tail.

joke photo without cell tube

Retention and Carry

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

lanyard installed lanyard installed lanyard installed

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.

lanyard installed and tailstanding

A pocket clip is included, too.

lanyard installed and pocket clip

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.

pocket clip shoulder

Clip hug!!

pocket clip hug

There’s no pouch or 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 which ships in the package.

included 21700 cell

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

included 21700 cell beside light

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

included 21700 cell installed

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!)

runtime graph turbo

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

runtime graph high runtime graph medium

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


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).

charge graph

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.

For reference, here’s a baseline shot, with all the room lights off and almost nothing hitting the sensor.  Also, here’s the light with the worst PWM I could find.  I’m adding multiple timescales, so it’ll be easier to compare to the test light.  Unfortunately, the PWM on this light is so bad that it doesn’t even work with my normal scale, with is 50 microseconds (50us).  10ms5ms2ms1ms0.5ms0.2ms.  In a display faster than 0.2ms or so, the on/off cycle is more than one screen, so it’d just (very incorrectly) look like a flat line.  I wrote more about this Ultrafire WF-602C flashlight and explained a little about PWM too.

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.

indicating e-switch

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

Here’s a UI 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 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.

bezel with relief

Check out the smooth reflector!

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.

turned on reflector and bezel shot

These beamshots are always with the following settings:  f8, ISO100, 0.3s shutter, and manual 5000K exposure.

Tint vs BLF-348 ( 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 219b BLF-348 because it’s inexpensive and has the best tint!


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


  • This light was provided by Sofirn for review. I was not paid to write this review.
  • This content originally appeared at  Please visit there for the best experience!
  • For flashlight-related patches, stickers, and gear, head over to!
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5 thoughts on “Sofirn SP35 Flashlight Review”

  1. Nice review. I have a Thrunite T2 and it sounds pretty similar except this is more throwy and uses a 3V led. Do you think the bezel can come off relatively easily to do an emitter swap?

    1. I did try to remove the bezel – hands only. I didn’t get it to budge. But then I’m very bad at that, so… you might have better luck!!

      1. Sharp in Singapore

        I tried using a Nitecore 21700 battery in mine but that battery was too long. I couldn’t get it to close fully and I didn’t want to risk compressing the end cap’s coil spring.

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