Sofirn SK31 Tactical Duty Flashlight Review

The Sofirn SK31 Tactical Duty flashlight features a very high output LMP LHP73B emitter and a tail e-switch with “mostly tactical” operation. Read on for testing!

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Official Specs and Features

Here’s a link to the Sofirn SK31 Tactical Duty flashlight product page.

Versions

This is the only version of the Sofirn SK31 Tactical Duty flashlight.

Price

The Sofirn SK31 Tactical Duty flashlight is available now for $57.99, a 28% savings from the MSRP of $79.99.

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What’s Included

• Sofirn SK31 Tactical Duty flashlight
• Sofirn 5000mAh 21700
• Charging cable
• Lanyard
• Holster
• Spare o-rings (2)
• Manual

Package and Manual

Build Quality and Disassembly

The Sofirn SK31 Tactical Duty flashlight feels like a robust flashlight! It offers a strong build quality with features that make sense for a tactical flashlight.

Among the important features for a tactical light: dual springs! Both the head and tail have thick springs.

A bit less common for a tactical or duty light is the inner sleeve/tube that allows the tail e-switch to operate. I did find the connection to be firm, though, and the light didn’t blink during strikes.

Size and Comps

150mm x 36mm x 27mm and 219g (with cell)

Here’s the light in hand:

Here’s the test light with the venerable Convoy S2+. This is a brass version, which is a good bit heavier than aluminum, but has the same dimensions: 24mm in diameter by 117.5mm in length.

Also in the photo above, my Standard Reference Material (SRM) flashlight is the Hanko Machine Works Trident, an 18350 light. While I have not reviewed or tested the Gunner Grip version seen here, I have tested a Hanko Machine Works Trident Total Tesseract in brass. I love the Trident, and it’s a striking contrast to the inexpensive Convoy S2+, another great SRM.

Retention and Carry

The Sofirn SK31 Tactical Duty flashlight includes a lanyard. This lanyard can be attached through the hole in the pocket clip, but a more secure place is through either hole in the tailcap.

A nylon holster is included. The light can not (or “should not”) be used while in the holster.

Power and Runtime

The Sofirn SK31 Tactical Duty flashlight runs a single 21700 lithium-ion cell. Sofirn includes a flat top, 5000mAh cell.

The cell goes into the light with the positive end toward the head. In case you forget that, there’s a silkscreened icon on the tailcap.

Below are a few runtime tests. Output doesn’t reach the 6800 lumen claim in my tests, but the light is very bright, especially for a single-emitter light. This LMP LHP73B IS bright! The output on high holds at well over 2000 lumens for minutes though, which is fairly fantastic. 

The stepdowns could be temperature-related, too, as the SK31 has built-in thermal protection.

The temperature lines in these charts are included as general context, not precise measurements. The values represent the range (min to max) during testing, but should not be taken as exact readings. A temperature sensor is not always attached to the bezel (or even the hottest spot, assuming that could be defined). Even with ideal placement, too many variables affect temperature to definitively state a specific max value.

Charging

The Sofirn SK31 Tactical Duty flashlight offers USB-C charging. It dispenses with a more traditional press-in charge port cover too, and uses a screw-down collar. The collar is very nice! Do note that the direction you twist to tighten the charge port cover is the same as the direction you twist to loosen the head. I found it better (though unusual) to hold the head and close the charge port. Or just be sure the head is fully seated after you tighten the charge port.

Sofirn includes a USB-C to USB-C charging cable.

C to C works fine, of course, but A to C works just as fine. Charging at 2A (from the source at 5V) is well within the safe range for this 5000mAh cell.

Modes and Currents

Mode	Mode Claimed Output (lm)	Claimed Runtime	Measured Lumens
Turbo	6800-1150	30s-120m	4589 (0s) 4267 (30s)
High	2400-1150-710	3m-90m-40m	2274 (0s) 2246 (30s)
Medium	1150-660-350	10.5h	1118
Low	350	66h	368
Eco	50	500h	73
Moonlight	1	–	0.87

Pulse Width Modulation

None of the six modes use PWM.

Click here to 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

Before we even get to the tail switch, we need to mention the lockout switch below. This toggle selects between lockout and unlock in the lockout state. The light does not operate at all.

For operating the modes, Sofirn provides this proud tail switch. It is an e-switch, despite how it looks.

The action is fairly deep, but it clearly feels like an e-switch.

There’s a “touch button” too. Or “the charging indicator doubles as a switch” – it’s novel. I don’t think I’ve ever seen a switch implemented this way. In fact, if you didn’t read it here (or read the manual), you might not realize this is a switch!

The user interface has a tactical and outdoor mode. Here’s a user interface table!

State	Action	Result
Any	Move lockout switch to locked	Off and locked
Lockout	Move lockout switch to unlocked	Unlocked (no change in off status)
Unlocked and off	Click tail switch	Outdoor Mode: On – mode memory Tactical Mode: Momentary strobe (momentary only, whether you click or hold it fully depressed)
Off, charging port open	Press “touch switch”	Touch switch indicates which mode is active: Tactical: Blue Outdoor: Orange
On	Click tail switch	Outdoor Mode: Off Tactical Mode: Momentary strobe (momentary only, whether you click or hold it fully depressed)
On	Tap tail switch	Outdoor Mode: Mode advance (all 6 steady modes) Tactical Mode: Momentary turbo (momentary only, whether you click or hold it fully depressed)
Unlocked on or off	Hold tail switch half-pressed >5s	Outdoor Mode: No change in state Tactical Mode: Turbo
Unlocked on or off	Hold tail switch fully pressed >5s	Outdoor Mode: Iterates light on or off Tactical Mode: Turbo

There’s a lot here, but the user interface is not complicated.

LED and Beam

Sofirn has used an LMP LHP73B emitter in the SK31. The emitter is coupled with a smooth reflector.

The bezel has some glass-breaking balls, and shaped so that light can escape while headstanding.

LED Color Report (CRI and CCT)

The CCT is cool white to very cool white, and the CRI is low. Not a surprise on a tactical light that has very high output!

CCT (Correlated Color Temperature) refers to the measurement of the color appearance of light, expressed in Kelvins (K), which indicates whether the light is warm (yellowish) or cool (bluish). A lower CCT (below 3000K) is considered warm light, while a higher CCT (above 5000K) gives cooler, bluish light.

CRI (Color Rendering Index) is a measure of how accurately a light source renders colors in comparison to natural sunlight. Scored on a scale from 0 to 100, higher CRI values indicate that colors appear more true to life and vibrant, similar to how they would look under the sun.

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. These photos are taken around 18 inches from the door.

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

Summary and Conclusion

The Sofirn SK31 Tactical Duty flashlight is a solid contender for a “tactical duty flashlight.” I like that there are two mode groups since I don’t have any need for a tactical light. Outdoor mode is nice because nothing is hidden behind multi-click actions. All six steady modes are right there in the main group! And there are no strobes in the outdoor mode! Very nice. The inner tube for the e-switch seems snug enough that it’ll withstand handholding, but it’s probably not ideal for weapon mounting. I also appreciate that the price is fairly low, at around $58.

The Big Table

Sofirn SK31 Tactical Duty flashlight
Emitter:	LMP LHP73B
Price in USD at publication time:	$57.99
Cell:	1×21700
Runtime Graphs
LVP?	Yes
Switch Type:	E-switch
Quiescent Current (mA):	?
On-Board Charging?	Yes
Charge Port Type:	USB-C
Charge Graph
Power off Charge Port	with cell: all modes without cell: lowest only
Claimed Lumens (lm)	6800
Measured Lumens (at 30s)	4267 (62.8% of claim)^
Candela per Lumen	9.9
Claimed Throw (m)	395
Candela (Calculated) in cd (at 30s)	1143lux @ 6.079m = 42239cd
Throw (Calculated) (m)	411.0 (104.1% of claim)^
Claimed CCT	–
Measured CCT Range (K)	6700-7400 Kelvin
Item provided for review by:	Sofirn
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 I like

• Reasonable price
• High output (even if it didn’t hit the claim)
• All 6 modes in the main group
• Outdoor group doesn’t have strobe
• The little indicator/touch switch!
• Very flat output (after any step-downs)

What I don’t like

• High CCT (very cool white)
• Low CRI
• Doesn’t hit output claim
• Tactical group user interface could use some tweaking

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Notes

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