Hi all! This is the first review I've written on this site before, so if you have any tips I'd be happy to read them!
Sofirn offered me the opportunity to review their newest ultraviolet (UV) light, the SP31 UV. They supplied me with this light for free, though they were clear that they just wanted a detailed review (and not necessarily a positive one). You can find more information about it on their product page: https://sofirnlight.com/sp31-uv-flashlight-p0151.html.
This light has two modes and a throwy beam profile, which sets it apart from other popular UV lights I’ve seen. It’s got a couple limitations that prevent me from recommending it as a general-use UV light, but I still quite like what Sofirn has produced here.
The Sofirn SP31 UV is another light from Sofirn’s SP31 line, this time sporting a 365nm LG UVA35W01RL00 emitter.
The flashlight has dual switches, two modes (low and high), and no other special functions.
What was included
The flashlight came with the usual accessories – a lanyard, two spare O-rings, a generic Li-ion USB charger, and a contact card.
No manual was included, but because the light only has two modes, it’s not hard to figure out the UI. Some estimated runtimes would have been nice, though.
The included cell is a 3000mAh Sofirn 18650, with a paper disk to prevent activation during transport. I measured the cell to be about 3.7V on arrival, which is a bit above the 30% state-of-charge mandated for shipping.
A discharge test indicated a capacity of 3069mAh, so its capacity is as advertised.
Construction
The flashlight is well-constructed and has no visible defects, as I expect from Sofirn these days.
Black anodizing coats the body, including the threads which allows for mechanical lockout. The forward-clicky tailswitch turns the light on/off, and the electronic side-switch controls the mode. An indicator in the button shows the battery level, and the clip is made of the usual strong spring steel.
The threads are nicely trapezoidal and come with enough grease to operate smoothly.
If you’ve ever owned an SP31 V2.0, then you’ll know exactly what to expect from this light – the hosts are identical.
The key difference is the emitter – here you can see the LG UV LED, with a much smaller surface area than the XP-L HI on the left. It also lacks a dome, which will no doubt make for a throwier beam profile.
Sofirn’s listing says this is a 365nm LG UVA35W01RL00 LED...but I have no idea what that is. I couldn’t find any official documentation, and it looks nothing like the emitter in my Convoy S2 LG UV.
Speaking of the Convoy S2 LG UV, the Sofirn is more than a centimetre longer than it on account of the Sofirn’s control mechanism and deeper reflector.
Another key difference is that the Convoy S2 LG UV has a ZWB2 filter that cuts down on visible light, whereas the Sofirn has clear glass. This will be quite noticeable later.
Performance
Comparing the beam patterns of the Convoy S2 and the Sofirn SP31, we see some familiar traits that are reminiscent of their non-UV counterparts; the Convoy S2 has a wide hotspot and more usable spill, and the Sofirn SP31 has a smaller, intense hotspot with weaker spill.
I measured a tailcap current for the Sofirn SP31 of 0.16A on Low and 0.51A on High. In comparison, the Convoy S2 drew 1.04A.
(My measurements of the higher currents may be a bit low, because I don’t have the best setup. But the relative power draw should still be valid.)
Against a non-fluorescent surface, the lack of a visible-light filter is apparent. The hotspot of the Convoy S2 is about as bright as the Sofirn SP31 on Low, despite the Convoy S2 emitting much more UV light.
The effect of the visible light can also be seen when looking for fluorescent marks on currency; in this comparison, the smaller fluorescent marks are harder to spot due to the Sofirn SP31’s visible light.
However, the tight hotspot does mean that the Sofirn SP31 UV is great for curing spots of UV-activated glue, without wasting light in the spill.
In such an application, the additional visible light really doesn’t have an impact on usability.
Summary
Strengths
- Well-constructed, and I always like a good forward-clicky switch
- Having two modes is a nice feature – no need to go full blast when you’re just checking a bill
Limitations
- Enough visible light to be distracting – including a ZWB filter or selling a compatible one separately would be a nice improvement
Trade-offs
- The tight beam is useful when targeting a specific area (e.g. Curing UV-activated glue), but is less suitable for scanning an area (e.g. Looking for fluorescent rocks or fluid residues)