REVIEW: Sofirn SD05 Scuba Diving Flashlight

A number of firsts, for me, happened in the last few weeks. Three that came at once were:

  1. receiving my first diving flashlight;
  2. this is my first 21700 battery format flashlight;
  3. HOW in Neptune's water world am I going to conduct a test on a diving light!??!

The third one presents a challenge as I'm not a scuba diver but I had some help (Thanks Henk4U2!).

The Sofirn SD05 Scuba Diving Flashlight caught my eye about a month back and so I started looking for more information about it, which was sparse, other than Barry creating a post. Not too long afterward, I received a message from 77Outdoor asking if I'd like to review one of three lights and, lucky for me, the SD05 was one of them!

I ordered the Sofirn SD05 on Amazon.

The purchase price of the light was reimbursed and the benefit to me is that I get to keep the light. In this review, I intend to provide my initial findings, observations and data with as little subjective information as possible.

The light is offered as a kit including the SD05, 21700 battery, charger, micro USB cable, battery adapter and lanyard along with the usual odds and ends.

The light's emitter is a Cree XH-P 50.2 at 6000K-6500K and coupled to the orange peel reflector, it produces a tight hot spot with plenty of spill.

As can be seen in the next few photos, the light appears to be comprised of three parts, the head, body tube and tail. There are two O-rings at the tail.

I see a (removable?) bezel and the driver appears to have been installed prior to inserting the battery tube into the head.

The three modes are changed with a magnetic contact ring with a simple rotary movement. There's a very slight bit of play in the ring but the light switches flawlessly. It sounds like anodized aluminum... well, on anodized aluminum. So, I surmise that even if sediment gets under the ring, it can be washed out.

And speaking of aluminum, look at those fins which, by the way, are 2mm thick with 3mm of space in between and ~3mm deep.

Looking inside the tube, from the tail to head, the driver looks like this:

On the other end, this is the tail cap:

Overall, the body of the flashlight is shaped to ergonomically allow one to spin the ring with your thumb and index finger and be held well with the rest of your fingers and palm.

The 21700 battery is stated to hold 4,000 mAh and I'd have to agree as I conducted a run-time test. Upon low voltage protection activation, the battery measured a potential of 2.8 V. I charged the battery at 1 amp and the internal resistance was around 26 mOhms per my Miboxer C4-12.

I have three brands of 21700 batteries on hand so the Samsung 50E, LiitoKala and Sofirn fit like this:

The measured currents at the tail for each battery with my DMM were:

Sofirn @ 4.19V- steady on 6.2A

Liitokala @ 4.19V- steady on 6.2A

Samsung 50E @ 4.19V- steady on 6.6A

I observed that the boost driver kept the current under 7.1A. At voltages below 4V and, if for more than a split second the current went higher than 7.1A, the driver would drop to various currents less than 3A with a corresponding drop in output. At first I noticed that this only happened with the DMM but then I loosened the tail, set the switch to high and tightened the cap again. Above a battery voltage of 4, it didn't happen but below, yes. I captured the step down with the lux meter and the light shining directly at it from 8.5 feet but the graph didn't look great. It'd be better if I closed the circuit with some wire and it set it up on a good tripod for better recording. Advanced Temperature Regulation (ATR) and the programmed turbo timer setting kicked in as specified.

The middle mode current was measured as 1.45A and low at 0.4A.

As mentioned earlier, I ran the light on high till the LVP kicked in. Measured with my best smart phone, here is the graph:

With a calibration factor of Lux value/3, (calibrated with my D4 on full 7135 and turbo output) I calculated a max output of 5,762/3= 1,920 lumens for this SD05 sample.

I've checked a number of my other lights to see if they met their specifications and a few did while others didn't. One of my favorite lights, the Sofirn (1,500 lumen) SP32A measured at 1,300 lumens.

Another method I used to measure output was this online lux to lumen calculator.

Inputs were:

I was looking for an output easily above 2550 lumens considering my DMM tail current measurements. As this may be one of the first reviews for the Sofirn SD05 on BLF, I look forward to other members conducting measurements with their equipment. However, comparing this light to my Sofirn SP33 with an XH-P 50.2 leaves me little concern that the Sofirn SD05 is producing the rated output.

And finally, the dunk test. The light was submersed at one foot in 68 quarts of water. I ran it on high and at every 3 minutes, toggled mid to high mode to make sure it ran as hot as possible (didn't really notice the step down). This was done for twelve minutes and then the light was shut off to contract and potentially suck in water for another 12 minutes. The light never even felt warm so I didn't expect an issue. Upon finishing the test, I pulled out the battery, examined the O-rings to see how far, if any, water got past them and all was good. No vapor presented itself under the AR coated lens. Here is my setup:

All in all, the SD05 is a solid light, exhibits good performance and within the limits of my 'equipment', is waterproof.


  1. a lot of light in a small package

  2. magnetic switch

  3. tail cap lock out

  4. double O-rings

  5. waterproof (at 100 meters?, I don't know)

  6. ATR

Wanted options:

  1. get rid of turbo timer

  2. 4000K-5000K emitter

  3. smooth reflector

I enjoy caving and even if it wasn't necessary, I'd still bring multiple lights. You certainly wouldn't want to be in this environment without backups

but the Sofirn SD05 would be one of them.

Let me know if you have any questions.

Thank you for reading!

Simple and strong add-on (from Atwood Rope MFG) for a simple and strong flashlight:

Thanks for the review!! Got any outdoor beamshots on this? :wink:

haha cool and thank you.
We offer 40% off code for this newly diving light. Any interested, just email Thanks.

That's a good idea! I'll look for a spot and add them. I swear the SD05 has tighter beam than the new SP33 and with a slightly larger reflector, it should.

Thanks for the nice review. I really think this is a goodlooking light and it has lots of performance going with it. Even as a non-diving flashlight it is compact enough to be interesting.

Great :wink:
If you can find that spot, please show us some shots :wink:
Thanks again!!

Found the spot(s)! Angry blue, warm and warmer... blinded myself. Lol

Thank you!

And I totally agree about the light!

Thanks for the review! Reserved all!

Edited 21:38:06, 09/13/2019

The fence is about 275 feet away.

Thank goodness she didn't run to the light!

This is a welcomed thread; I just purchased the Thorfire TD01 and while it is only 18650 powered, it is really has same basic setup with the rotary switch. I purchased it for the waterproof depth though I’m not a diver.

The main difference between the two appears to be the lumen outputs and the rotary levels; the Thorfire’s first “notch” is high as opposed to low with the Sofirn. I have, however, noticed a slight delay of sorts that allows me to twist all the way to low before the light actually turns on. This must be done pretty quickly though…

@Hoosh, thank you for pointing out the TD01. Yes, similar lights.

Last night when I took the beam shots, it was kind of bound to happen but it fell one time on the ground and the soil is a lot like sand. Just from that minor drop, enough got under the switch ring to bind just a bit. I washed it twice but still doesn't feel exactly the same. I noticed some instructions with the Thorfire product that mentioned lubricating the switch so I'm curious if anyone can tell me what lubricant is recommended. One concern I have is that some lubricants may eat at the anodization. Others may trap grit under the ring.

It would be great to hear from any divers on the forum.

Thanks for posting the pictures :wink: It gives a glimpse of what it does! Being a simple light, I am tempted to buy it and leave it at my parents home for them to use . I’m only afraid of heat on high mode…

Thanks for posting :wink:

You're welcome! I added a few more from a 'formal' camera and the light was mounted. The heat is something but nothing like a D4. Medium isn't too bad.

With regard to your parents (and not to spoil the fun of getting one of these SD05s), you could get them some Sofirn SC31s and replace the XP-G3 with some SST-20s. Perhaps one with a 5000K and the other with 3000K or 4000K. The low would be much lower than this dive light and the switch's so-called breathing feature could help them in locating it at night. Not much heat either. I suspect you have a number of models in mind but that's what I bought for my mom.

Um abraço!

how far deep can this light tolerate under water ?

I don't think anyone has confirmed the 100m specification but this is the deepest I've seen the light in use: Video Review

I have just ordered the light :slight_smile:
Will try it down to 60-70m just like I did here:

Too bad the turbo mode is going to high after 3 minutes…

I recently tested the SD05's thermal regulation.

It seems to work like a charm. I did not manage to drive it beyond 55°C (ATR thermal threshold for stepdown) even when restarting the high-mode. It would be nice to run the SD05 without time-triggered stepdowns.

A dive with this light would be awesome! Exactly what the forum needs.

About the modes, you may switch it up again to turbo.

Looking forward to your dive!