The Sofirn SK31 was sent to me directly by SOFIRN for review.
For technical details and to purchase the flashlight:
https://www.sofirnlight.com/products/so … flashlight
SOFIRN has recently introduced the new SK31 tactical flashlight. Crafted from AL6061-T6 aluminum alloy for excellent mechanical durability, it offers two modes: Tactical and Outdoor.
The Sofirn SK31 is powered by a replaceable 21700 5000mAh lithium battery, providing a maximum runtime of 500 hours (Moonlight mode at 1 lumen).
Measuring 150mm (5.90") in length and weighing 219g (including the battery), the SK31 features a three-switch system (a mechanical tail switch, a tail toggle switch for lockout, and an electronic side switch) and 6 brightness levels (Turbo, High, Medium, Low, Eco, and Moonlight), in addition to special modes: Strobe, SOS, and Beacon.
The SK31 delivers a maximum output of 6800 lumens and a peak beam intensity of 39,006 cd, achieving a maximum throw of 395 meters.
The Sofirn SK31 is IPX8 certified and impact-resistant up to 1.5 meters.
Its compact size and features make it an ideal companion for signaling, locating, and emergency assistance at night, as well as for night walks, night fishing, camping, and more.
Key Features:
• Utilizes a Lumenpioneer (LMP) LHP73B LED with a maximum output of 6,800 lumens
• Peak beam intensity of 39,006 cd and maximum throw of 395 meters
• Switches: tail switch, rotary tail switch (lockout), and side switch for mode switching (Outdoor or Tactical)
• Maximum runtime of up to 500 hours
• Customizable beam function allows users to set different beam profiles to meet various lighting needs
• Intelligent Li-ion battery charging circuit with a hidden USB-C charging port supporting 5V/2A charging
• Brightness level and power indicators show current brightness and remaining battery charge
• High-efficiency constant current circuit provides stable output
• Two-way stainless steel clip included
• Optical lens with double-sided anti-scratch coating
• Constructed from AL6061-T6 aerospace-grade aluminum alloy
• HA III military-grade hard-anodized finish
• IPX8 rated
• Impact resistance up to 1.5 meters
Specifications
Length: 150 mm / 5.90"
Head Diameter: 27 mm / 1.06"
Weight: 219 g / 7.72 oz (battery and accessories included)
Warranty Service
We first attempt to resolve the issue. In the unlikely event of a defective product, we may advise customers to return the product to Sofirn for repair or replacement.
Within 30 days of purchase: contact the original seller for repair or replacement. Flashlights: within 1 year of purchase
Batteries: within six months of purchase
The warranty does not cover normal wear and tear, modifications, misuse, negligence, accidents, improper maintenance, or repairs performed by anyone other than an authorized retailer or Sofirn itself.
Contact Sofirn for repair or replacement via:
Email: service@sofirnlight.com
Facebook Group: sofirn deals group
Facebook Page: www.facebook.com/sofirnlight
The Sofirn SK31 arrives in a soft, light-colored box. The box specifies the model, color, LED type, and color temperature. Inside the package, I found the Sofirn SK31 with the clip and battery installed, a USB-C charging cable, spare O-rings, a lanyard, and a pouch.
The Sofirn SK31 is constructed from aircraft-grade aluminum alloy with a military-grade HA III hard-anodized finish. It features an IPX8 waterproof and dustproof rating (withstanding continuous immersion in water deeper than 1 meter) and is impact-resistant up to 1.5 meters. The markings on the flashlight are of good quality.
The Sofirn SK31 fits well in the hand; it measures 150 mm in length and weighs 219g (including battery and clip). The body features attractive knurling that ensures a secure, excellent grip, even when the flashlight is wet or when wearing gloves. It immediately conveys a sense of solidity and high-quality construction.
The Sofirn SK31 consists of three parts and is operated by a three-switch system; the main switch is located on the tail and protrudes, preventing the SK31 from standing upright (tail-standing).
The Sofirn SK31 features a steel clip; a carrying lanyard is also included in the package.
The SK31 offers various carrying options: held in the hand (secured by the included lanyard), carried in a jeans pocket or backpack using the clip, or placed in a holster worn on the belt.
The internal, removable battery is a Sofirn-branded 5000mAh 21700 lithium cell, offering a maximum runtime of 500 hours (Moonlight mode) in the SK31.
Here are the battery specifications (data sourced from a test review on BLF):
Battery type: 21700
Battery capacity: 5000 mAh (standard), 4900 mAh (minimum)
Battery voltage: 3.6 V
Maximum discharge current: 10 A (but can handle up to 15 A)
Diameter: 21.7 mm ± 0.2 mm
Length: 70.9 mm ± 0.2 mm
Weight: 72 g ± 4 g
Nominal capacity: 5000 mAh at 0.2C discharge current
Minimum voltage: 2.50 V
Maximum voltage: 4.20 V ± 0.03 V
Standard charging current: 0.2C (1000 mA)
Maximum charging current: 0.7C (3500 mA)
Maximum discharge current: 2C (10000 mA)
Initial internal impedance: ≤ 30 mΩ
The charging time in QC mode, as measured by me, is approximately 2 hours and 50 minutes (max 2.6A).
The Sofirn SK31 can also be powered by non-proprietary batteries, although a discharge current of at least 16A is recommended.
Regarding battery contacts, there is a plated spring at the head and another at the tail. The battery should be inserted in the standard way, with the positive terminal facing the head of the flashlight—a direction also indicated by a small symbol near the tail.
It is possible to unscrew the tailcap to access the plated negative terminal spring.
At the head of the Sofirn SK31, there is an aggressive bezel featuring a crenellated design with tungsten beads—crafted from PVD-coated stainless steel—and a smooth reflector. At the center sits the Lumenpioneer LMP LHP73B LED in a cool white version (6500–7000K), delivering a maximum output of 6800 lumens and a maximum beam range of 395 meters.
The LMP LHP73B LED offers high performance, featuring a design composed of sixteen small LED chips arranged in a 4x4 square on a gray substrate.
The Sofirn SK31 features a 3-switch system. The two-stage rubber button controlling the available output levels is located at the tail and produces an audible click; also at the tail is the button (selector) for locking and unlocking the flashlight. Finally, by unscrewing the ring beneath the head, one finds the third button, which allows for the selection of the operating mode: Outdoor or Tactical.
The mode button allows you to switch between Tactical Mode (steady blue light) and Outdoor Mode (steady orange light).
Upon powering on, the current battery level is displayed by the battery indicator.
- Steady green = 75%–100%
- Flashing green = 50%–75%
- Steady red = 25%–50%
- Flashing red = 1%–25%
Charging indicator (battery compartment):
- Charging = steady red
- Fully charged = steady green
- No battery installed = alternating red/green flash
- Low battery indicator: when the battery level is low, the indicator will automatically flash red.
On the opposite side of the switch is the retractable USB-C charging port.
SOFIRN SK31 next to other flashlights.
From left: Armytek Viking PRO MAX, SOFIRN SK31, Nitecore P27iX e Brinyte PT16.
USER INTERFACE (UI)
The user interface of the Sofirn SK31 is simple and easy to remember. The SK31 features two modes: Outdoor and Tactical. It has 6 brightness levels, plus special modes (Strobe, SOS, and Beacon). These special modes can be activated when the Sofirn SK31 is in Tactical mode. The SK31 includes low-voltage protection: if the flashlight is on and the battery level drops too low, it automatically turns off to preserve battery life. It also features thermal protection: during operation, if the flashlight’s temperature reaches a preset threshold, the output is automatically reduced to regulate the temperature.
The brightness levels are well-spaced, starting with a 1-lumen “Moonlight” mode. Below is a diagram taken from the manual.
Lock/Unlock / Mode Switching
Rotate the rear rotary switch to select Lock or Unlock.
When unlocked, press the touch button to switch between Tactical Mode (solid blue light) and Outdoor
Mode (solid orange light).
When the flashlight is on, selecting Tactical Mode defaults to maximum output, while
selecting Outdoor Mode defaults to Moonlight mode. The indicator will show the current mode
for 5 seconds before automatically turning off.
Tactical Mode: On/Off / Medium / Maximum
Half-press the rear tactical button for maximum output; release within 5 seconds to
turn off.
Half-press and hold for more than 5 seconds to maintain maximum output.
Half-press again to cycle between Medium and Maximum. Fully press the rear button to turn off.
Tactical Mode: Strobe / SOS / Signal
Fully press and hold the rear button to activate Strobe; release within 5 seconds to turn off.
Fully press and hold for more than 5 seconds to maintain Strobe.
Half-press again to cycle through Strobe → SOS → Signal.
Fully press the rear button to turn off.
Outdoor Mode: On/Off / Moonlight / Eco / Low / Medium / High / Maximum
Flashlight off: fully press the rear button to turn on and access the memorized
brightness level.
Flashlight on: half-press the rear button to cycle through Moonlight → Eco → Low → Medium →
High → Maximum.
Fully press the rear button to turn off.
Beam and Runtime
The Sofirn SK31’s beam pleasantly surprised me with its illuminating power and quality; it is clean, free from dominant tints or aberrations, and features a white hue that isn’t overly cool. The light output is impressive—it certainly outperforms the competing XHP70.3—and I would compare it to the Luminus SBT90.2, as it features a large Light Emitting Surface (LES) that produces a surprisingly bright beam.
Using the OPPLE Light Master Pro, I took measurements of the CCT (correlated color temperature) and Ra (color rendering index) at various output levels. Flicker falls within the safe green range. The beam’s color rendering is within the standard range, with an Ra value of approximately 70.
Here are the measurements:
TURBO (6800 lumens): measured CCT is 6385, Ra is 69.9, Duv = 0.0047
HIGH (2400 lumens): measured CCT is 6231, Ra is 68.9, Duv = 0.0064
MEDIUM (1150 lumens): measured CCT is 6143, Ra is 68.6
LOW (350 lumens): measured CCT is 6057, Ra is 68.2
The Sofirn SK31 has a powerful beam; the candela values (lux at 1 meter) I measured at a distance of 5 meters roughly correspond to those stated by Sofirn, albeit with a lower Turbo output. I tested replacing the Sofirn battery with a Samsung 40T and achieved better results. No PWM is visible to the naked eye.
Some measured values (listed values in parentheses):
TURBO 6800-1500 lumens (39006cd): 33259cd – 38880cd with Samsung 40T battery
HIGH 2400-1150-710 lumens (14400cd): 16516cd
MEDIUM 1150-660-350 lumens (6806cd): 8090cd
LOW 350 lumens (2166cd): 2627cd
ECO 50 lumens (324cd): 494cd
Using a FLIR thermal camera, I measured the heat distribution on the body of the Sofirn SK31 in its most powerful mode—Turbo at 6800 lumens—at 1, 2, and 6 minutes after activation. The heat distribution is good. With this LED, the Sofirn SK31 quickly reaches high temperatures in Turbo mode. After the first minute, the temperature on the flashlight body drops due to a reduction in light output, which is effectively managed by the flashlight’s electronics.
Runtime tests were conducted indoors at an ambient temperature of approximately 26°C, using the included battery—a fully charged Sofirn 21700 5000mAh cell.
It should be noted that the values shown in the graphs serve primarily as a reference, as the tests were performed using hobbyist-grade equipment and environmental conditions that differ from those found in a laboratory setting.
The Sofirn SK31 features good regulation. Runtime performance with the 5000mAh Sofirn battery is roughly in line with the manufacturer’s specifications.
Tests were conducted using Turbo, High, and Medium modes.
Let’s look at the first 10 minutes:
VIDEO Unboxing and Use
CONCLUSIONS
The Sofirn SK31 was a pleasant surprise. I really liked the feel of the flashlight; it is well-built using quality materials. I was particularly impressed by the remarkable beam width, thanks to the LMP LHP73B LED. The package is comprehensive, including both the battery and a holster.
Regulation is good, and runtime is decent. Recommended.
Thanks for reading the review.
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