Review: Sofirn SP31 v2.0 18650 dual-switch

This Sofirn SP31 v2.0 was provided by Sofirn for review. It's currently available on Amazon in the US as a bundle with battery and charger. It is usually offered unbundled at a lower price, and may also be available on other regional Amazon sites or Sofirn's Aliexpress store.

A full album with extra images is available at https://imgur.com/a/kniVxXX

Quick Review

The Sofirn SP31 v2.0 is a dual-switch 1x18650/2xCR123A light with a Cree XP-L HI emitter. It resembles a Fenix PD32, but it's slimmer and costs half as much. For those familiar with this very popular category, that's probably all I need to say for you to make a decision about this light. For the rest of you, a review follows.

The SP31's classic dual-switch configuration uses a tailswitch for power. Half-press is momentary, and a full press until the switch clicks locks it on. A side switch cycles through five modes in a low to high order. Nearly every major flashlight manufacturer produces a light in this configuration with a straight tube-shaped body an inch (25.4mm) in diameter, usually with a price around $50-60.

The SP31 v2.0 distinguishes itself with a 24mm bezel and a price under $30. It further distinguishes itself from its low-cost competition, the Wowtac A1S by having an efficient constant-current buck driver instead of a linear driver with PWM. My only serious complaints are that it has a needless timed stepdown in addition to its sensor-based thermal regulation, and that it only comes in cool white as of this writing.

  • + Slim profile
  • + Long throw for the size
  • + Efficient electronics for the price
  • + Battery indicator light is uncommon at this price point
  • - Cool white only
  • - Low CRI
  • - Unnecessary timed stepdown

Good use cases

  • General household/car flashlight
  • Throwy EDC light
  • Spare light for others to use
  • Platform for emitter swaps

Bad use cases

  • Situations where preserving dark adaptation matters
  • Situations where color is important

Details and technical analysis

Versions

The SP31 v2.0 only comes one way, but Sofirn offers a bundle with a battery and charger. This is the bundle.

Accessories

The SP31 v2.0 includes a lanyard, pocket clip, and spare O-rings. The bundle version also includes a Sofirn branded 3000 mAh 18650 battery, a 1A USB charger resembling the Xtar MC1 Plus, and a USB cable.

Modes and user interface

State Action Result
Off Half-press tailswitch Last-used (momentary)
Off Full-press tailswitch Last-used (constant)
On Press tailswitch Off
On Press sideswitch Next mode (L -> H)
On Hold sideswitch Strobe
Strobe Press sideswitch SOS

Loosening the head or tail a quarter turn mechanically locks out activation.

Output and runtime

Advertised performance is with an unspecified 3500 mAh 18650 battery. Tested performance is with a Sony VTC6 3000 mAh 18650 battery unless otherwise noted.

Mode Advertised Lumens Estimated Lumens Throw (FL1 meters) Graph Advertised Runtime Time to 80% Time to 50% Time to 10% Tailcap current (mA) Efficiency (lm/W)
Eco 5 4 15 - 291 hours - - 273 hours 11 mA -
Low 50 45 49 - 26.8 hours - - 32 hours 93 mA -
Medium 160 135 86 - 9.75 hours - - 11 hours 270 mA -
High 500 430 153 graph 221 minutes 143 minutes 146 minutes 170 minutes 1.03 A 101
Turbo 1200 901 222 graph 157 minutes 3 minutes 3 minutes 140 minutes 2.7 A 85

Advertised throw is 225m on turbo. Sofirn lists throw for every other mode as well on its official site and my measurement is within 3 meters every time. It's a bit odd that the throw matches so closely but the output does not. I wonder if Sofirn re-used output numbers from a previous version of this light that used the more efficient, less throwy XP-L2 LED.

There is no low-voltage shutoff, though the indicator switch gives a warning, followed by a series of stepdowns to low.

Turbo has an abrupt timed stepdown to high after 3 minutes. There is also sensor-based thermal regulation which triggers a much more gentle rampdown to about 70%. I've seen similar behavior before on the Thrunite TH30, but that light makes nearly four times the output and can't possibly be used for an extended period of time without overheating unless immersed in cold water. The SP31 could be used at full output without overheating in a light breeze.

Additional graphs

  • Resetting the timed stepdown - numbers over 100% are probably user error on my part, disturbing the position of the light relative to the sensor. This shows the thermal sensor at work starting from the second reset.

Light quality

The SP31 v2.0 is unapologetically cool white. It's probably a bit over 6000K, but it's a very pure cool white without off-tints, large shifts in tint across the beam or artifacts. The outer spill has a bit of purple, but it's not really noticeable outdoors. People who don't mind cool white will probably like it, but it does wash out colors.

Output is fully current-regulated with no PWM in any mode.

White wall

  • https://imgur.com/hpRZNWt.jng

Outdoor

  • https://imgur.com/7ASQ4Fq.jpg
  • https://imgur.com/0I0tCI5.jpg

Construction

The SP31 v2.0 is solidly built. The aluminum is machined precisely, and there are no visible toolmarks. The springs are stiff, the threads are smooth and square-cut. The finish is a bit prone to scratching, but no worse than many lights with considerably higher price points.

Sofirn advertised IPX8 water resistance to 2 meters for 30 minutes. A brief immersion did not result in any signs of water ingress.

Ergonomics

The SP31 v2.0 has typical ergonomics for an 18650 dual-switch light. The side switch is easy enough to find by feel with bare hands, but would present an issue with gloves. The tailswitch is somewhat proud - enough to prevent tailstanding. Sofirn has informed me that this has been changed on new-production models and future samples will tailstand. The body is knurled adequately for grip, but not aggressively.

In the pocket, the SP31 v2.0 is thinner than most 18650 lights. It's not a huge difference since it still needs to accomodate an 18mm battery, but it's enough to notice. The clip is a design common to many Chinese manufacturers. It would go well with a shorter tailcap, but allows 32mm of flashlight to stick out in this case.

Batteries

Any quality 18650 battery will work in the SP31 v2.0. Two CR123As are also supported. The battery included with the bundle is a Sofirn branded protected button-top with an advertised capacity of 3000 mAh. I measured 3015 mAh. The Sofirn battery has warnings written on it in English, Russian, and Ukranian.

The charger from the bundle is a single-slot USB charger resembling an Xtar MC1 Plus. It charges at 1A given an adequate USB source and terminates correctly.

Modification potential

Emitter swaps are easy in the SP31 v2.0. The bezel attaches at the base of the reflector, granting easy access to the emitter. There's a small amount of threadlocker on the bezel, but I found it easy to break free.

I was hoping to delay the review until my shipment of Luminus SST-20s arrived, as I suspect those would preserve the long throw of this light while adding CRI and nicer tint. They haven't, so I tried the Samsung LH351C. Throw drops to 185m and output to 830lm. The beam is a fairly neutral 5000K with no artifacts and relatively even tint. The outer spill does have a little purple from the AR lens, but it's not bad.

Most 3V high-power emitters should work well in the SP31 v2.0, from popular options like the Nichia 219C and Samsung LH351 series to exotics like the ultra-throwy Osram White Flat. Its buck driver will have good efficiency and proper regulation regardless of forward voltage.

Recommendations to the manufacturer

  • Remove the timed stepdown. With a thermal sensor, the stepdown just makes this light worse.
  • Offer neutral white. When only offering one tint, 5000K is an ideal choice, as nobody hates it even when it's not their favorite.
  • Consider LED manufacturers other than Cree. Samsung's high-CRI LH351 series is particularly worthy of attention from manufacturers.