Sofirn SP31 UV 18650 Flashlight Review
The Sofirn SP31 UV (Ultraviolet) 18650 flashlight has been available for a little while and I got my hands on one! I seem to have gone from not having any UV lights for years to having multiple on my desk all at once! Read on for some thoughts and testing.
Official Specs and Features of the Sofirn SP31 UV 18650 Flashlight
Here’s a link to the official product page.
Versions
Technically there are a number of versions of the SP31. There’s the regular SP31, a v2.0, and this UV version. But of the UV versions, there is only this version.
There are two packages available, though. One is with cell and charger (seen here) and one is just the bare UV flashlight.
Price
Without cell, the Sofirn SP31 UV 18650 flashlight sells for $23.74. With cell and charger, you’re adding only $3 – $26.74. The cell and charger are certainly worth the $3. You can buy yours here.
Sofirn SP31 UV 18650 Flashlight Short Review
This UV flashlight is much more like a flashlight converted into a UV output light, than a dedicated UV flashlight. The beam is throwy (for UV) but not all that “clean” – there’s a lot of output that isn’t UV. That said, at $26, this is still a great deal. It has plenty of UV for your UV needs, and the dual output, dual switch interface is great.
Sofirn SP31 UV 18650 Flashlight Long Review
What’s Included
- Sofirn SP31 UV (Ultraviolet) 18650 flashlight
- Sofirn 3000mAh 18650
- Spare o-rings (2)
- Lanyard
- Charger (1 bay, micro-USB)
- Charge cable (USB to micro-USB)
- Manual
Package and Manual
Build Quality and Disassembly
By measure of the quality of the knurling, I’d rate the SP31 UV to be priced “about right.” That’s not to say the build quality is bad. In fact, there are touches in this light that probably put it in a higher class than “$23.”
This is a UV (ultraviolet) flashlight. And a bit unusual in that it’s a two-mode variety. There’s a smooth reflector, and the beam is quite tight.
Sorry for the dirty tailcap in this photo and some others. Things were dirty on the workbench!
The head has some cooling fins. Not all that much cooling is really required, though. The light is not driven with all that much current.
This bezel (above the switch) is removable too. You might wonder, after the Convoy S2+ UV I just reviewed, could that ZWB2 filter fit in this Sofirn? No it can not. The filter is just a little bit too wide. And I mean just a little bit – maybe 0.2mm or something.
The tailcap has ample knurling.
The UV flashlight will headstand, but the bezel is smooth so no output can be seen.
Threads on the tail end are very nice and beefy. They’re anodized, square-cut, moderate length, and not overly lubricated.
The head end is much the same. In fact, the cell tube is reversible.
Both head and tail have nice thick springs, so if you opt-out of the $3 Sofirn cell, you should be good to use any other type 18650 you have on hand.
Size and Comps
Officially 72g, 113.5mm length. Sofirn doesn’t state the diameter, but this is a 18650 tube light, so probably around 25.4mm.
If the flashlight will headstand, I’ll show it here (usually the third photo). If the flashlight will tailstand, I’ll show that here, too (usually the fourth photo).
Here’s the test light with the venerable Convoy S2+. Mine’s a custom “baked” edition Nichia 219b triple. A very nice 18650 light.
And here’s the light beside my custom engraved TorchLAB BOSS 35, an 18350 light. I reviewed the aluminum version of that light in both 35 and 70 formats.
Here’s the Sofirn SP31 UV (just a quick note here – I’ve tried to call this light the “SC31 UV” so many times, and also the “SP31 Pro UV” so many times…. if I make that mistake please forgive me, and let me know! 😀 )…. Here’s the SP31 UV with the Convoy S2+ UV.
With the square-cut threads, there are some interchangeable parts between the two. The tailcap of the SP31 UV will fit on the body of the Convoy, for example.
Here’s the SP31 UV with the SC31 Pro. This is the reason I’ve typoed the name so much. The lights (and names) are quite similar! But of course, a UV light doesn’t need Andúril, so it’s reasonable this would have a different build and different user interface.
Retention and Carry
A friction fit pocket clip is included with the SP31 UV. It’s an ok clip. Nothing special, but does the job of a pocket clip.
The clip itself is not reversible, but the cell tube is. So you can reverse the clip by just flipping the cell tube.
Also included is a lanyard, which attaches through two holes in the tailcap. The holes are on one side only.
Power and Runtime
Power is provided by a single lithium-ion cell. If you buy the package, you’ll get a 3000mAh button top 18650, which is perfectly good for this flashlight.
Since my luxmeter is completely unresponsive to the UV wavelength, I can’t really do any runtimes for the Sofirn SP31 UV 18650 flashlight. Based on bench power testing, however, I can say that the indicating switch starts flashing red at 2.7V.
The package also ships with this single bay, micro-USB powered 18650 charger. Since I couldn’t do runtimes and didn’t have any post-runtime depleted cells, I also didn’t test this charger. However, it’s the same charger as seen in another review – the SP33 New.
An appropriate cable is included – USB to micro-USB.
Modes and Currents
| Mode | Mode Claimed Output (lm) | Claimed Runtime | Measured Lumens | Tailcap Amps |
|---|---|---|---|---|
| High | – | – | – | 0.71 |
| Low | – | – | – | 0.15 |
Pulse Width Modulation
No pulse width modulation on either mode – that’s good.
Here you can 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
The primary interface with the SP31 UV is with the tailswitch. It’s a forward mechanical clicky.
The switch is usable with gloves, and low profile enough that it allows tailstanding.
Secondly is the side e-switch. This switch can indicate red or green and is proud on the side of the head.
Here’s a user interface table!
| State | Action | Result |
|---|---|---|
| Off | Click Tail Switch (TS) | On (Mode memory) |
| On | Click TS | Off |
| Off | Click Side Switch (SS) | No action |
| On | Click SS | Mode cycle |
| Off | Hold TS | Momentary mode memory |
LED and Beam
The emitter is an LG UV 365nm LED. I don’t know anything more about this emitter. Whatever it is, it’s at the base of a smooth reflector.
The beam is quite throwy, really, and provides a tight spot of UV output.
As with the Convoy pictured above – I’m still very sensitive to UV and don’t like to overexpose myself. So here are a few beamshots using the Sofirn UV flashlight.
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.
I compare everything to the KillzoneFlashlights.com 219b BLF-348 because it’s inexpensive and has the best tint!
Conclusion
What I like
- Good build quality (especially for the price)
- Multiple modes of UV
- Dual switch interface
- Complete package for around $26 is good.
What I don’t like
- Seems to have a large amount of the visible spectrum in the ultraviolet output
- Not sure a two-mode light really needs a dual switch interface. (I’d take a smaller version with no mechanical switch, for example.)
Notes
- This light was provided by Sofirn for review. I was not paid to write this review.
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