Sofirn SK40#

Specifications
Introduction
Torch in use
Build quality
LED, bezel, lens and reflector
Size and comparison
User interface
Batteries and charging
Performance
Thermal Images
Beamshots
Conclusion
Price
Product page

Specifications#

Brand/model	Sofirn SK40
LED	Luminus SFT70 6000-6500K
Maximum lumens	3,200 lm
Maximum beam intensity	84,583.3 cd
Maximum throw	580 m
Battery	21700
Onboard charging	Yes (USB-C)
Material	Aluminium
Modes	5
Blinkies	Strobe, SOS, Beacon
Reflector	Smooth
Waterproof	IP68
Review date	May 2026

Introduction#

The Sofirn SK40 Tactical Torch has a forward-clicky tail switch, a side switch with a battery status indicator, and USB-C charging. It is powered by a single 21700 Lithium cell. The Luminus SFT70 LED and the smooth reflector produces a throwy beam.

Sofirn kindly provided this torch for review. I have not been paid for this review nor have I held back my opinions of this torch.

Packaging#

The torch comes in a white box with an image of the torch on the front of the sheath and specifications on the back.

The following is included in the box:

Sofirn SK40.
Sofirn 21700 3.7V Li-ion 5000mAh cell.
USB-C to USB-C cable.
Two spare o-rings.
Lanyard.
User manual.

User manual#

Torch in use#

The Sofirn SK40 is a decent size for my large hands.

The design of the tube provides a little bit of grip but it feels like the torch might slip out of my hand while wearing gloves.

The pocket clip makes it easy to hang the torch off a backpack strap.

The tube is small enough to fit most scope mounts.

The torch can tail stand when the tail switch is clicked but it will topple over when the torch is off.

Build quality#

This Sofirn SK40 is made of alumimium and it has a matte black anodised finish.

There are no sharp edges.

The pocket clip cannot be reversed.

The tail switch has a little bit of play.

The threads are anodised and turn smoothly.

The head and tail need to be tightened down onto the tube properly or Turbo mode may not work.

The springs at each end allow flat top 21700 cells to work. Longer protected button top cells do not fit.

LED, bezel, lens and reflector#

The Sofirn SK40 has a Luminus SFT70 6000-6500K emitter.

The LED is surrounded by a gasket and has a smooth reflector pressed down against it by a glass lens and a bezel.

The lens appears to have an anti-reflective coating.

CCT, CRI, and duv#

I have taken Correlated Colour Temperature (CCT) and Colour Rendering Index (CRI, RA of R1-R8) measurements with the torch positioned two metres away from an Opple Light Master Pro III (G3).

The CCT is around 6000K, the CRI is around 66 and the Delta u, v is positive (green).

The beam has an intense white hot spot surrounded by a slightly green corona with a flower pattern and a wide spill.

Mode	CCT (K)	CRI (Ra)	x	y	Duv
Eco	5760	65.2	0.3260	0.3603	0.0124
Low	5855	65.3	0.3239	0.3554	0.0110
Medium	5973	66.0	0.3215	0.3496	0.0093
High	6191	67.3	0.3174	0.3411	0.0070
Turbo	6631	69.6	0.3106	0.3276	0.0036

Calculate Duv from CIE 1931 xy coordinates

Dimensions and size comparison#

Dimensions#

I took the following measurements using a digital caliper.

Measurement	Unit (mm)
Length	147.11
Head diameter	40.13
Tail diameter	27.48

Weight#

I took the following measurements using a digital scale.

Weight	Unit (g)
Torch	136.81
Battery	66.28
Torch and battery	203.09

Size comparison with its competition#

From left to right: Sofirn SK40, Sofirn C8L, Convoy L21B, Armytek Predator Pro Warm, Acebeam T35 Coyote

User interface#

The Sofirn SK40 is controlled by a forward-clicky tail switch and an electronic side switch.

It has a Normal mode and a Tactical mode.

There are three levels (Low, Medium, High) in the main group. There are shortcuts to Eco and Turbo. And there are three blinky modes: Strobe, SOS and Beacon.

Normal Mode#

State	Action	Result
Off	Click the tail switch	On (mode memory)
Off	Half press and click the tail switch	Turbo
Off	Hold the side switch and click the tail switch	Eco
On	Click the tail switch	Off
On	Click the side switch	Cycle (Low, Medium, High)
On	Double click the side switch	Turbo
On	Triple click the side switch	Strobe
Strobe	Double click the side switch	Cycle (Strobe, SOS, Beacon)
On	Long press the side switch	Tactical Mode

Tactical Mode#

State	Action	Result
Off	Click the tail switch	Turbo
Off	Half press and click the tail switch	Strobe
Off	Double click tail switch	Strobe
On	Click the tail switch	Off
On	Click the side switch	Cycle (Medium, Turbo)
On	Double click the side switch	Cycle (Strobe, SOS, Beacon)
On	Long press the side switch	Normal Mode

Mode memory#

There is mode memory for Low, Med and High.

If Eco or Turbo were the last used modes then the torch will revert to Low, Med or High.

Strobe#

Strobe has an alternating frequency.

Strobe, SOS, Beacon

I measured Strobe, SOS and Beacon with a Zoyi ZT-706S oscilloscope using High Speed mode.

Battery level indicator#

The battery level indicator will appear for 5 seconds when the torch is turned on.

Colour	Battery level
Green	70% - 100%
Red	30% - 70%
Red flash	0% - 30%

Low voltage protection#

There is low voltage protection.

The light turned off at 2.68V.

I tested low voltage protection by powering the torch with a bench power supply and by lowering the voltage from 4.20V until the light turned off at 2.68V.

Pulse Width Modulation#

I did not notice any visible PWM (flickering).

I measured the PWM of the light with a Zoyi ZT-706S oscilloscope.

Eco, Low, Medium, High, Turbo

What I like about the UI#

Normal and Tactical mode groups.
Shortcut to Eco from off.
Shortcut to Turbo from off.
Shortcut to Strobe from off.

What could be improved#

I like the Tactical mode as it is.

Batteries and charging#

Battery#

The Sofirn SK40 arrived with a flat top Sofirn 21700 3.7V Li-ion 5000mAh cell.

The cell was isolated with a piece of plastic to prevent accidentally turning the torch on.

I tried the following cells:

Cell	Top	Compatible?	Comment
Sofirn 21700 3.7V Li-ion 5000mAh	Flat	Yes
Wuben ABD4800 21700 3.6V Li-ion 4800mAh	Button	No	Too long.
NEXTORCH 21700 5000mAh USB-C	Button	No	Too long.

Charging#

The torch has USB-C charging.

Power supply: PinePower Desktop USB-C
USB Meter: ChargerLAB Power-Z KM003C
Room temperature: 20 C

It took 4 hours 21 minutes to charge the the battery in the torch from 2.86V to 4.21V at a rate of 5V/1.9A.

The charging status indicator is red while the torch is charging and it becomes green when charging is complete.

Power supply compatibility#

I tried the following power supplies with the USB-A magnetic charging cable:

Power supply	USB Type	Protocol	Does it charge?
Apple 20W Power Adapter	USB-C	PD	Yes
Google Pixel Power Adapter	USB-C	PD	Yes
PinePower Desktop	USB-C	PD	Yes
PinePower Desktop	USB-A	QC	Yes
PinePower Desktop	USB-A		Yes

USB-C to USB-C charging works.

Performance#

Specifications from the manual:

ANSI / PLATO-FL1	Eco	Low	Medium	High	Turbo	Strobe	SOS	Beacon
Output (lumens)	10	150	500	1,500 + 1,100	3,200 + 1,100	3,200	500	3,200
Runtime	290h	18h	4h 50min	5min + 2h 10min	1min + 1h 50min
Beam Distance (metres)	31	142	260	410	580
Beam Intensity (cd)	244.2	5,058.3	16,950.0	40,421.7	84,583.3

I used the included 21700 cell for the following tests.

Lumen measurements#

I used a bench power supply to measure the current at turn on for most modes. I used a Zoyi ZT-QS7 clamp meter to measure the current for Turbo.

Mode	Amps at start	Specs	Lumens @turn on	Lumens @30 sec	Lumens @10 min
Eco	0.01 A	10	8	8	8
Low	0.23 A	150	158	158	156
Medium	0.88 A	500	514	509	503
High	2.92 A	1,500 + 1,100	1,290	1,265	1,217
Turbo	10.70 A	3,200 + 1,100	2,716	2,502	1,003

Note: Lumen measurements may be off by 10% with my DIY lumen tube.

Standby drain#

There is no standby drain due to the tail switch.

Runtime graphs#

I used my own DIY lumen tube with a TSL2591 sensor and forked bmengineer’s project RuTiTe to record runtimes.

The room temperature was approximately 20 C.

Runtime#

Here is a summary of the runtime results:

Mode	User manual	Runtime	Turn off	Final voltage
Turbo	1min + 1h 50min	1h 56min 6s	2h 24min 11s	2.84
High	5min + 2h 10min	2h 22min 30s	2h 25min 35s	2.86
Medium	4h 50min	5h 35min 34s	5h 35min 34s	3.01
Low	18h	17h 51min 14s	17h 51min 14s	3.02
Eco	290h	10min +	10min+