Diving Light Comparison: SD05, WK20S, WK20

I just returned from a week of freediving on Santa Catalina Island, in Southern California, and I thought I would pass along some observations about three new-ish dive lights: the Sofirn SD05, the Wurkkos WK20S, and the Wurkkos WK20. Since these lights have been thoroughly reviewed in other threads, I will focus on their underwater functionality. I have no pictures, sorry, because I need both hands just to operate the underwater camera.

I tested and compared the three lights at depths of 0 to 40 feet, on daytime dives, in dark shadow under ledges and inside caves. In pitch blackness, the lights might appear brighter, and might throw farther than in my experience. Catalina typically has very clear water, and I would estimate visibility of 30 to 80 feet on my dives. Nevertheless, I consider the practical range of these small lights to be about 25 feet, limited by absorption and backscatter.

Physical Design and Performance
Mechanically, all three lights functioned perfectly, and remained watertight after a total of about 12 hours in sea water over four days. The SD05 is both shorter and lighter than the Wurkkos lights (which are identical physically) and accommodates a larger capacity 21700 cell. The Wurkkos lights have thicker aluminum in the head and battery tube, but I don’t see this as an advantage underwater. The Wurkkos lights also have a nicer wrist lanyard; I would never trust the cheap metal snap clip that comes with the SD05, but that is easily remedied. All three lights are manufactured by Sofirn it seems, and all claim to have HAIII anodizing; but, if so, it is very thin. So, I give the Sofirn the edge in physical design and fuel capacity.

User Interface
Regarding the interface, there are significant differences. The Wurkkos lights use a side button, which cycles the output with each click. To turn the light off, you must long press the button. This is not very intuitive, but pretty easy to adjust to on land. However, it is troublesome underwater. About half the time, when I thought I had turned a Wurkkos light off, I did not hold the button down long enough, and the output just advanced to the next level. So, I would try again. Consequently, next time I turned the light on (it has memory), I was unsure what level I was on. I found myself constantly clicking through a full cycle because I couldn’t tell otherwise which level was high. Another issue with the button is that, if you release the light (with the lanyard attached to your wrist), when you grasp the light again, you must fumble to find the button.

The Sofirn SD05, by contrast, uses a magnetic ring, which is fantastic. Since the ring encircles the head, it does not matter how you grab the light, the ring is always at your fingertips. In addition, the ring and head have white markings so that you can easily tell at a glance what output level the light is on. But the ring is so easy to operate that I rarely needed to look: you simply turn the ring left until it stops and the light is off, turn right until it stops and the light is on high. If you are careless, it is conceivable that you could get grit under the ring that would cause it to bind, but I think the advantages far outweigh a little bit of extra care. In terms of UI, I would rate the Sofirn as notably superior underwater.

Light Performance
As for output, the first thing I discovered is that more is better underwater. At any distance beyond ten feet, I found myself using only the highest settings, and the ~2000 lumen SD05 and WK20S were more usable than the 1000 lumen WK20, e.g., for spotting lobsters deep under ledges or in crevices. None of the lights got hot on high, in 70 degree F water. So, the three-minute timed stepdown on the SD05 is a nuisance (since it also has thermal stepdown), but, in practice, it was a non-issue for me (but this might be different during extended night diving). The three lights have virtually identical reflectors, in terms of width and depth, but the WK20 is SMO, and the other two are OP, with a slightly more aggressive texture on the SD05. Despite this, the three lights have very similar, very usable beam profiles underwater, with fairly broad hotspots, and some spill that fades at very short distances. I was surprised that the big quad-die XHP50.2 emitter in the SD05 did not appear to have a noticeably larger hotspot than the Wurkkos lights underwater, as it does through air.

I was also surprised to find that, underwater, I disliked the 3000K CCT of the WK20, which I find very pleasing on land. Rather than making things look warm, it made them look dingy. Also, the warmer CCT did not appear to cause any less backscatter through water than the cooler emitters. I slightly preferred the CCT of the WK20S (nominally 5300K) to that of the SD05 (nominally 6000K), but the difference was only noticeable side by side. Underwater, the tint of all three lights seemed equally neutral, with no noticeable Duv, either greenish (+) or rosy (-). The tint shift of the XHP35 HD emitter in the WK20S, which is prominent in white wall hunting, was not noticeable underwater.

For underwater use, I would rank the Sofirn SD05 first, because of the compact size, superior interface, larger battery capacity, longer run times, and bright output. The WK20S is also a good choice if you can get used to the button interface. With its lower output and warm CCT, combined with the button interface, I would not recommend the WK20 as a dive light. However, for use as a tough, waterproof utility light, I would probably reverse my order of preference. The Wurkkos lights are more heavily built, and look like they could withstand more abuse. On land, I find the warm CCT of the WK20 is quite pleasing, and it has five output levels (vs. four for the WK20S and three for the SD05), including moonlight. This makes it very versatile. By contrast, the lowest output level for the SD05 is 300 lumens, which is great for underwater, but very limiting for a utility light.

I’d be happy to try to answer any other questions.

Thanks for the clear observations, and for pointing out what is different underwater from on dry land (which I would not have a clue of).

Kewl, tnx!

My only underwater experience with flashlights would be testing them in a utility sink. :laughing:

Excellent review of dive lights from a diver! Makes a huge difference.

Thank you for the solid write up! Been years since I’ve dove, but my needs are having something I can toss in a kayak or my boat and not have the Ocean dissolve in 3 min or less:-) Waterproofness and being hardy is #1 consideration for me. I have the Sofirn SD05 on order using one of Fin’s recent Banggood codes, was planning on using an 18650 cell instead of the 21700 of which I own none. Did you happen to confirm that is a workable thing? Factory says it is.

Yep, 18650’s work fine in the SD05: protected or unprotected, flat top or button top.

I’ve noticed this on land as well. Not sure I buy into the “backscatter” thing

Glad an experienced diver took a look at some diving lights. And they survived the test!
I’m quite certain that a lot of so called diving lights are not even worthy of that title.

Just to satify my curiosity: what lights do you use yourself? And as a backup light?

I apologize, Henk4U2, for not responding sooner, but I’m afraid my answer to your question will not be very informative. Yes, I am an experienced diver, but I am a FREE diver (no tanks). In this sport, anything you have to carry, whether it is a camera, a sling, or a flashlight, reduces the depth and travel on each dive. Also, I never dive at night. So, for my purposes, a small, single cell light—which would normally be considered a backup light when SCUBA diving—is the only practical option. Over the years, I have used a variety of lights underwater, including (briefly) a McGizmo Haiku. But I consider the Sofirn SD05 and Wurkkos 20S to be the most useful lights I have used to date, primarily because of their high output.

For now, I prefer the compact size and ring switch of the SD05, but I plan to continue using both these lights. I should have mentioned this in my original post, but the ring on the SD05 rides on small bearings, and I have no idea, yet, how resistant they are to corrosion. And the switch is not really user serviceable. In my case, I am not too worried about this, because (as with my camera housing) when I leave the water I immediately put my flashlights (while still wet) into a fresh water rinse bag, and soak them for an hour. The switch on the Wurkkos 20S, on the other hand, can be disassembled. And the button and spring can be cleaned, and lubed with an anti-corrosion coating. So, if you plan to use one of these lights on a boat or in a kayak, the Wurkkos might be more durable.