Introduction.
The SK31 is a compact powerhouse of a light with 2 separate modes, tactical and everyday. It’s controlled by a single tailswitch, but also has a hidden mode-select switch, plus a lock on the tailswitch to, you guessed it, lock it out when not in use to help prevent fires.
It uses a 21700 lithium cell and has onboard USB charging.
It also has a rather unique user interface (UI) which stirred up a bit of controversy online.
In The Box.
The box is a no-frills cardboard box with nice graphics, and all the goodies are in a formed plastic tray to keep everything safe and secure.
The light is cradled in the tray, and all the goodies are stored in the underside, with a folded paper “lid” tucked in to keep things from falling out when you slide the tray out from the box.
First and foremost is the light with included cell, plus insulating disc for transport which needs to be removed.
Underneath is the one instruction sheet in a pile of languages (pdf available on Sofirn’s site!).
Also included, a pretty nice holster that has a D-ring on top, as well as an incredibly nice molle strap secured with a snap AND Velcro! My only grex is that it’s a bit too spacious for the light. Elastic side-straps keep it snug, but it’s still swimming around in there. It’d be perfect for a shorter 26650 light, though.
In addition are the C-to-C charging cable, and packet with O-rings and lanyard.
It comes with a 2-way(!!!) clip already attached. So yes, you can attach this big donk to the brim of your hat if you want to. 
First Impressions.
Seriously, I’ve known good to great anodisation over the years, and thankfully, gone forever are the days of pits and voids. The SK31 is no exception. Flawless smooth semigloss ano, edges that are crisp but not sharp, smooth threads, and just a fit and finish that’s just about perfect.
The tailswitch is firm and not mooshy. It needs to distinguish cleanly between a partial press and a click-through. Lots of button travel makes that easy. There’s no play in the button at the start of travel, no wiggle, no “bubble”, nothing. Clicking through is pretty decisive as well. Simply put, there’s zero ambiguity in what you want vs what the switch does.
The lock switch is pretty secure. You need to work it from the top, not side, so it’s best handled two-handed. It’s not for casual or frequent use like a mode switch or power switch, rather, only when securing the light against accidental activation and later readying it for use.
There’s a captive ring which covers the mode-select switch and charging port, which is also buttery smooth to tighten and loosen. It’s also O-ring sealed.
The front glass has a slight purple reflection, so we have anti-reflective coating as well.
The specs indicate the emitter is 6500K, but it doesn’t look that cold. The color temp looks quite nice at higher power levels. At lower levels, there seems to be a bit of green, but even at its lowest level, it’s not that noticeable, or objectionable. The green might be due to the AR glass?
All in all, it’s pretty impressive, even at first glance.
The Beam.
As mentioned, the ostensible 6500K doesn’t seem that cold, and the hotspot seems quite a bit warmer.
The beam has a somewhat bullseye pattern, and while the hotspot is nice and uniform, the spill has a bit of light, dark, light, rings as you go from center to periphery.
The hotspot isn’t a pencil-beam by a longshot, nor is it “floody”. It’s great at close- to intermediate range, but is usable at longer distances due to it just being a light cannon and getting more reach through brute force! 6800lm packs a lot of punch!
The Modes.
There are two basic mode groups, tactical and everyday.
Tactical is essentially just turbo and strobe, but you can get to low, sos, and beacon if you want.
Everyday is 6 levels from moonlight through turbo.
Moonlight is quite usable as actual moonlight, but the compact hotspot still throws quite a bit.
Then there are “eco”, low, medium, high, and turbo. Spacing is pretty good, making the light useful for most situations.
Power!
The come-with 21700 is rated 5000mAH, and a capacity test clocked it at 4548mAH at 1A up and down, within the 10% range.
After charging via its onboard charger and pulling the cell, the cell was at 4.15V, great for longevity by not overcharging the cell.
The indicator light glows red when charging, green when finished.
The User Interface.
Ohhhh, the user interface… I’ve seen reviews that mentioned it, and lots of hating on it, and honestly, I was all prepared to, and even expecting to, hate on it as well. But I’ve taken some time to just play with it extensively, for quite some time, and it’s… grown on me? I might not necessarily love it, but I understand it. And it’s been pretty useful to me as-is.
First things first. You switch between modes by unscrewing the captive ring and pressing the button/indicator. In everyday mode, that’s it. It’s easy. In tactical mode, the indicator’s off, and I was trying pressing, holding, keeping the light on while pressing, etc., and it would only randomly switch modes.
Solution? Press twice! Once to wake it up, again to switch modes. Derrr.
Blue indication is for tactical mode. Orange (red+green blended) is for everyday mode.
That out of the way, let’s go through tactical mode. Half press gets you momentary turbo. Click-through gets you momentary strobe. Holding either for 5sec or more turns it constantly on, and you can release the button and only give it a click to turn it off.
This… confusion… is what gets people hating on it. And I get it, I really do. But after you’ve used it a while, lit up whole alleys like daylight, you get used to it and it becomes sort of muscle-memory-ish. Yeah, it does take a while, and I’ve only used turbo in tactical mode because I hate blinkies except for beacon.
Oh, once in turbo-constant, you can click to alternate between turbo and low. In strobe-constant, you can cycle through sos and beacon as well.
Now for everyday mode, it’s just click-through for on/off, and half to cycle through the 6 brightness levels. It has mode memory to remember the last setting.
In fact, it remembers everyday level even after going to tactical and then back to everyday!
My only BIG grex about everyday mode is that other than cycling through brightnesses when on, half-press is a completely dead function when off. When off, half-press does nothing. Not momentary remembered level, not momentary moonlight, nothing. Huge wasted opportunity! I’m hoping this gets fixed in any revision.
So all in all, I can’t jump on the “this UI is a dealbreaker!!” bandwagon. Once you get used to it, it’s really not that bad. Everyday mode especially is quite usable just like any mech-switch tail-clicky. On/off with a click, half to cycle, done. When off, it’s like any other reverse clicky in that momentary does nothing. But what’s missing is that it can do something, but doesn’t.
Tactical is confusing at first, but once you get that muscle-memory, you just use it without thinking about it too much.
It’s not the greatest UI, but it’s not the worst. I’m perfectly okay using it.
Addendum: the lock switch will force off everything, just like unscrewing to physically lock out the light. If it’s on, it turns off. If it’s off, it stays off
I’ve seen mention that the switch loosens after repeated use, but I haven’t noticed that at all. It’s still a firm twist in either direction.
Summary And Wrap-Up
First and foremost, it’s a great piece of hardware. Fit and finish is nigh perfect. Switchfeel is great and unambiguous. Threads are buttery smooth.
The beam could be made a bit more even and not as ringy or bullseye-y, and I’d love to see what a narrow angle TIR lens in that size might do.
The UI can be improved, and I suspect that given feedback, it’s already in the process. But as-is, it’s still perfectly usable. Ironically, even though I have more of an issue with tactical, I usually keep it in that mode because I like momentary-on. If everyday mode had momentary-on, I’d definitely keep it in that mode.
And almost 7000 lemons is a huge punch to throw when it’s dark out. I remember when we had those high winds and I heard a huge crash that sounded like it was right outside the window, I went out to check both sides of the house, and that blast of light let me see into next week. And nope, nothing fell off the house, thankfully.
And it seems to be at a pretty nice price-point for all that oomf in a compact package like it has. Looking at it, I’d guess 2000, 2500, maybe 3000 lemons, but not almost 7000! That’s downright incredible!
While you don’t have to use it in tactical mode as a tactical light, everyday mode is incredible, and any occupation like plumber, contractor, house inspector, exterminator, etc., where you need a reliable light that gets great runtime at modest power but can be cranked up to 11 when needed, would find the SK31 indispensable.
And if you do use and would need tactical mode, half-press for turbo and click-through for strobe, that part of the UI is unbeatable.
I’d definitely recommend it!
Direct link to the puppy on Sofirn’s website:
[Some pix pilfered from Sofirn’s website…]