This is the SK31, a new tactical style flashlight made by Sofirn. It has a LHP73B as the main emitter, screwable aluminum USB-C cover, powered by a single 21700 battery, 2 button design and a lockout dedicated selector!
*Sofirn informed me this is prototype version that doesn’t have the Eco (50 lumens) mode, they said this is the only major change from my version to the final one, but be aware the final product can have some small changes.
• My opinion:
The SK31 is a major improvement on Sofirn tactical flashlights, it combines most of the requested “tactical” features other Sofirn products lacked. It’s really nice to see Sofirn using more constant current drivers, the LHP73B was one of the best additions on this flashlight, as it has a stunning output and a very clean tint; the screwable aluminum cover is also awesome, as it protects the USB-C and mode button from water really well and are more resistant than those rubber caps. This is probably the best Tactical flashlight Sofirn has ever made.
I think the lockout button placement is kind of odd, I would prefer to swap the lockout and mode button places. And the included battery should be higher CDR for a LED like the LHP73B, I recommend that you use at least 20A CDR battery on the SK31.
| PROS | CONS |
|---|---|
| Aluminum screwable USB-C cover | Lockout button “bugs” sometimes |
| Tungsten pins on bezel | The included battery has lower CDR than recommended |
| Potted USB-C for better water resistance | Battery indicator is hidden under the screwable cover |
| Efficient Buck Driver | |
| Easy operation on the tail button | |
| Very efficient LHP73B emitter with no green tint |
• Box contents
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SK31
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Holster
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21700 Battery
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USB-C to C charging cable
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Stainless steel clip
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2x extra O-rings
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*User manual (Wasn’t included in my package)
• Price
The SK31 is currently priced at $50.19 in the Sofirn AliExpress Store and $52.99 on Sofirn Official Website
• Body and build quality
Colors/Material Options: The SK31 is available only in aluminum with black anodizing.
Material: The main body is entirely made of 6061-T6 aluminum alloy. The bezel is made of black PVD coated stainless steel as well as the clip.
Threads: The battery tube threads are squared and anodized, this means the flashlight has mechanical lockout, also, there is an inner tube inside of the battery tube, that is actually what makes contact with the driver. The bezel threads are trapezoidal.
Clip: The flashlight comes pre-installed with a dual way clip, it only has one position and it can be rotated around it. It’s made of stainless steel with a black PVD coating.
Tail stand and rolling: It cannot tail stand as the rubber button is higher than the tabs on the tail cap; it can head stand though. With the clip the flashlight doesn’t roll much as the clip prevents it, without it the flashlight will roll on your desk.
AUX lights: The SK31 has an AUX light under the mode button; it serves to show at which mode you currently are (Tactical or Outdoor) and to show the battery level everytime the flashlight is turned ON. This light is hidden under the threaded aluminum cover on the flashlight head, so you will have to expose the USB-C to weather to see the battery level or change the operation mode.
Buttons: Sofirn advertises it as having 3 buttons, but it actually has 2 buttons and a lock switch.
- Mechanical tail switch: The main button is the mechanical switch on the tail cap covered by a rubber button, it turns ON/OFF the flashlight and cycles through the brightness levels.
- Hidden mode button: The second one, the mode button, which is hidden under the threaded aluminum cover, it’s function is to change the operation mode of the flashlight (Tactical - Blue light / Outdoor - Orange light) and to show the battery level.
- Lock switch: The third button is the lock switch, which only locks/unlocks the flashlight, it is located on the tail cap below the main button for easy access. Sometimes the lockout button seems to “bug” and the flashlight doesn’t turn ON even when it’s unlocked, flipping it to “locked” and after “unlocked” again solved this problem for me.
Battery contact: Contact is made with the battery by two gold-plated springs one on the tail cap, the other on the driver, the springs are thicker than usual Sofirn flashlights, as they have to withstand higher currents for the LHP73B LED.
Bezel: The bezel is made of stainless steel with a black smooth PVD coating, and it has a special feature: Tungsten spheres on it for breaking glass or other structures without damaging much the bezel.
Water Resistance: This flashlight has IPX8 rating as most Sofirn flashlights, but this one has way better water ingress protection than most of them, because instead of a rubber cover on the USB-C this one has a whole rotating aluminum cover with an O-ring inside! The rubber cover on other Sofirns will degrade on the future, the rotating cover with the O-ring will last much more and the O-ring is way easier to replace than the rubber cover on other light, bonus points for this.
Size comparison: On the left is the Brinyte PT16A (21700), on the middle the Sofirn SK31 (21700) and the Convoy S2+ (18650) on the right.
• Weight and size
Weight:
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Without battery: 154.1g
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With battery: 223.3g
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Battery (Button top Sofirn 21700 cell): 69.1g
Size: 156.1mm x 36.0mm x 29.2mm (height x head diameter x tail diameter)
• Battery, runtime, and charging
Battery: The SK31 uses a 21700 battery, both button or flat top, a Sofirn 21700 battery is included in the package. The included battery only has 10A CDR and 15A pulse discharge rate, and LHP73B would need more than 15A, according to the datasheet, to produce the advertised 6800 lumens, so maybe it’s a good idea to get a high CDR battery to run this flashlight on Turbo, because it probably won’t get to the advertised 6800 lumens with the included battery.
Battery Indicator: It has a battery indicator on the mode changing button, it’s hidden under the screwable USB cover. The battery indicator lights up as it follows:
| Color | Battery level |
|---|---|
| Green | 75-100% |
| Flashing green | 50-75% |
| Red | 25-50% |
| Flashing red | 1-25% |
Charging: This flashlight features USB-C charging, the port is protected under the screwable aluminum cover. It charges at 5V 3A maximum, at this power it will charge in around 3h. When the battery charge is complete the mode button will light up green, when charge is in progress it will light up red, if the battery is not installed correctly the mode button will flash green and red.
• Modes, Runtimes, Throw, Candela:
Modes: The flashlight has 6 modes officially, but the unit I received only has 5.
| Mode | Brightness (Lumens) | Runtime |
|---|---|---|
| Moonlight | 1 | 500h |
| *Eco | 50 | 66h |
| Low | 350 | 10h30min |
| Medium | 1150 - 660 - 350 | 90min - 25min - 70min |
| High | 2400 - 1150 - 710 | 3min - 90min - 40min |
| Turbo | 6800 - 1150 | 30s - 120min |
*Eco mode was not included on my flashlight cycle.
Turbo: Turbo is pretty bright with advertised 6800 lumens. To reach this brightness you will probably need to use a higher CDR battery than the included one, as the current to reach this number of lumens is more than what the standard Sofirn battery can provide.
Moonlight: Thank you Sofirn! After testing so many flashlights with poor moonlights, finally another flashlight with good moonlight was released! The 1 lumen mode is good, I would prefer even lower moonlight, like 0.1 lumen, but for a tactical light I think 1 lumen is nice.
Blinkies: This light features Strobe - SOS - Beacon that can only be accessed on the tactical mode by holding the tail cap switch pressed for 5 seconds, and half clicking to cycle between the blinkies.
Lockout: Lockout on this flashlight is pretty easy to access, as it has a dedicated button just for it. You just need to flip the lockout button tab to locked or unlocked. The lockout button position is kind of weird, and I didn’t like much, I think there could be a more useful button there, like a dedicated brightness level button like the SK30.
Throw: The flashlight has a beam similar to the SK30, with a defined wide hotspot and a lot of spill, but it still manages to throw, especially with the high lumen LED this flashlight has. Sofirn advertises it to throw at around 395m with 39000cd.
• Emitter, reflector and CRI:
Emitter: This flashlight uses the LHP73B emitter in 6500K, a very powerful and efficient emitter that can deliver a lot of power in this host. The tint is pretty good for a cool white emitter, almost no green/yellow tint at all! The LED itself is very floody, but with the reflector Sofirn used it has some throw on it.
Beam profile: The beam is not very clean, it has some rings and small artifacts on it, but from my testing they’re only visible from up close.
CRI: The LHP73B has standard 70 CRI.
Lens: There is an anti-reflexive coated glass lens in front of the reflector.
Reflector/TIR: It uses a smooth reflector for improved throw.
• Beamshots Camera settings:
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18mm lens 1" F8 ISO800
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(The trees at the back are at a distance of around 100m)
SK31 - Turbo (*6800 lumens)
SK31 - High (2400 lumens)
SK31 - Turbo (1150 lumens)
I always try to match what my eyes can see on the beamshots, so camera settings may vary. All pictures were taken immediately after the flashlight was turned ON.
• Driver and UI
Driver: It has an efficient constant current “Buck” driver, I didn’t notice any PWM on it.
UI: The UI is easy to understand and use. The lockout button and the mode button have the same function and operation on both modes, only the tail switch has a different operation:
Outdoor mode: The tail button turns the flashlight ON/OFF when fully clicked, when the flashlight is ON half clicking the tail button will cycle between Moonlight - *Eco - Low - Medium - High - Turbo.
Tactical mode: The tail button activates momentary Strobe when fully clicked; when half clicked it will go to momentary Turbo, if held for more than 5 seconds it will maintain the mode until you fully press it again.
Low Voltage Warning: The flashlight will turn OFF when the battery voltage is too low.
Reverse Polarity Protection: Yes.
Temperature Control: The SK31 has standard temperature control, if the internal temperature gets too high, around 50-55°C the flashlight will dim down to prevent driver/LED damage.
A special thanks to Sofirn for sending this flashlight for me to review!
*I am not being paid to do this review, everything here is my honest opinion.
Thank you for reading my review <3