Today I’m reviewing the updated version of Sofirn’s SD05 flashlight. This is my first diving light and my first light with a rotating switch.

About the light

The SD05 is advertised as a diving light and is waterproof to 100m. It uses a 6000K (cool white) CREE XHP50.2 LED and puts out 3000lm on high. It takes a single 21700 sized cell, though will work with 18650 cells too.


You can buy the Sofirn SD05 on Amazon UK (£39.99, with cell and charger). Only an older version of the SD05 comes up in a search on Amazon US at the moment but the new one may be available when you’re reading this. It’s also available from Sofirn’s shop directly, either just the light or with cell and charger.


The original SD05 version stepped down from high after 3 minutes to keep the light cool, which isn’t so useful in a diving light. Sofirn listened to customer feedback and have released a new SD05 flashlight without the timed step down. The old version was listed at 2550 lumens and the new one claims 3000 lumens. When purchasing, make sure you get the new version, as some places still have the old in stock. Sofirn could have called the new one something else to help differentiate the 2 versions, such as SD05B.

There don’t seem to be any different LED options available.

Sofirn SD05 specs

EmitterCree XHP50.2 LED, 6000K-6500K
WaterproofIPX8, underwater 100 meters
Case Material6061Aircraft-grade aluminum alloy
Power Source1* 21700 battery
Net weight120g (Excluding battery)
I measured 119g without the cell and 187g with
Working voltage3- 4.5V
Dimension119mm(length) × 37.5mm(head)
I measured 119.7mm length, 37.5mm head and 29.0mm body diameter
Sofirn SD05 official specs

The physical light

What’s in the box

Sofirn picked a plain cardboard box for the SD05. They seem to use this for their larger packages and have a nicer printed cardboard for their smaller ones.

In the box you’ll find:

  • SD05 light
  • Manual
  • 21700 cell
  • Sleeve for 18650 cells
  • 2 o-rings
  • lanyard
  • Micro USB cable
  • USB charger

Appearance and quality

The SD05 has 2 O-rings at each end of the body tube to help with waterproofing. There’s 2 o-rings, 1 either side of the glass too. The box only comes with 2 spares but they’re easy to source if you need new ones.

The body tube is asymmetric, with much thinner threads on the head end (the same size as the bezel threads). I have no idea why they went with 2 thread sizes.

There isn’t any knurling, aside from a few bumps.

The SD05 has fairly thick springs at either end. This means it can take a range of different length cells and doesn’t flicker when it’s shaken.

Physical comparison

The SD05 takes a 21700 cell, so is a bit bigger than most 18650 lights. Here’s the Sofirn SD05 next to an Emisar D4 (18650 cell), an Imalent MS03 (21700 cell) and a Nightwatch NSX3 (21700 cell). It’s nicely sized and comfortable to hold.

Carrying and everyday use

The SD05 comes with a standard lanyard, which is attached at the tail at the side (so it can still tail stand). There’s no clip but the light’s probably a bit big for most pockets anyway.

Underwater use, swimming

This is a new section in my reviews. I have a few lights that are IPX8 rated (so should be waterproof enough to be in water for 30 minutes at 2 meters depth) but don’t have any that are designed primarily for use underwater. I’m by no means a diver (I’ve never been anywhere near the 100m depth rating of the SD05) and I rarely go in water when it’s dark or deep enough to need a flashlight.

I wanted to put the SD05 through its paces though, so I took the SD05 to a nearby river.

I’d normally be nervous putting electronics in water, especially a river that was so murky. The SD05 did fine though and allowed me to see fish and stay out in an inflatable dinghy well past dusk. I have to admit, having a flashlight underwater is pretty cool at night. The 3000 lumens allowed me to see over 2 meters through the cloudy parts of the water. I lowered the light on a string down 2 meters a couple of times too. The river wasn’t anywhere near as deep as the 100m rating that Sofirn give.

When I was done I gave the light a rinse and dried it. As expected, there weren’t any signs of water ingress.

Interface and switch

The SD05 has a rotating “switch” instead of a button, presumably because it’s hard to make a physical button fully waterproof. I’ve never used a flashlight with a switch like this before. It’s incredibly intuitive and doesn’t need any explanation.

The switch feels very slightly loose and has 0.5mm play either way at each mode but this doesn’t seem to be a problem. The switch changes mode when it’s about 2/3 of the way towards the mode you’re changing to, whether that’s up or down. This is good, as it means there’s no half way point for it to flicker at.

Using the Sofirn SD05 switch with gloves

The switch has very slight knurling and can be rotated with just a thumb, albeit slightly awkwardly. Using the switch with gloves on works fine. Not a problem using both thumb and index finger though. More knurling would mean use with just a thumb or finger would be easy.

The SD05 uses a magnet in the switch (a reed switch) to work out which mode it should be on. That means the light can be turned on with any magnet! This is unlikely to be an issue in most cases but is good to know.

SD05 flashlight being switched on using the magnetic tail cap of an Emisar D4

Cell and charging

The SD05 came from Amazon with a cell, cell sleeve and a charger.

The cell is a Sofirn branded flat top 21700, that says it has a capacity of 4000mAh and current of 40A. The cell measures 21.5mm diameter by 70.8mm long. The 21700 cell protrudes about 5mm from the tail. My XTAR VC4 said it put 3829mAh into the cell from an almost full discharge, which is pretty close.

If you’re actually using the SD05 for diving then buying a 5000mAh 21700 cell would be worthwhile for 25% extra run time. Changing cells underwater is not recommended.

The sleeve is designed for 18650 cells but it’s a bit wide, with an innder diameter of 19.5mm. This didn’t seem to be a problem though and a flat top 18650 worked fine with it: sitting flush and making a good connection with the springs.

Almost any 21700 or 18650 should work with this light. The only cell I had that didn’t fit was a 77.6mm 21700 cell with integrated charging.

The single cell USB charger is basic but seems to do the job. It’s rated at 1A and a quick check showed it pulled 0.85A via from the included micro USB cable when the cell was getting full. The charger is spring loaded and should charge cells between 31mm and 72.5mm and mentions cells from 26650 to 10440. The charger is only 19g, so would make a good travel charger for lithium cells.

Light output


There’s only 3 modes but they’re nicely spaced. The modes seemed fine for use in water but 300lm is quite high for general use. When packing up after being out on the river, the 300lm low was a bit bright.

ModeLumensRuntime (claimed)
High30001h 38min
Medium9002h 30min
Low3008h 16min
Modes and run times

Run times

The SD05 uses a 3V LED and takes a 3.7V cell so it can use simple driver. There’s no voltage boost circuit here, which means the output reduces as the cell voltage drops. My light meter setup isn’t calibrated but does accurately show relative light output changes.

Normal run times

Left out on a hot day on high the light will step down from 3000 lumens after a minute. The supplied cell then lasted over 2 hours above 600lm before the low voltage protection kicked in. Holding the light and on a cooler day will probably let the light stay brighter for longer, meaning the cell won’t last as long. The SD05 got up to 55°C on high.

Water cooled

I tested the SD05 in water, to check the thermal regulation and also just because I could. The SD05 stayed above 2000lm for about 30 minutes, then started to drop off and only lasted 45 minutes on high. The output change as the voltage drop is more visible in the graphs. You can also see the low voltage protection kicking in, dropping the light to medium, then low and giving some warning flashes.

LED and beam, PWM

The SD05 has a 6000K XHP50.2 LED and orange peel reflector. The large head makes this slightly throwy (270m), with a smooth transition from spot to spill. 6000K is way too cool for my liking but neutral white 3V XHP50.2 LEDs seem hard to come by.

The driver uses PWM to dim the light in different modes. The PWM isn’t noticeable by eye but some beam shots showed the PWM much more than other lights I have.

Similar lights

Searching Amazon for diving lights gives all sorts of results, including some zoomable Shadowhawk clones that are definitely not waterproof. If you’re buying a light for diving then make sure you get one from a reputable company.

Here’s some alternatives I’ve found that are rated for 100m+

Sofirn SD053000lm270m21700magnetic rotating ring
Wurkkos DL405000lm400m2 x 26650magnetic side switch
Acebeam W30500lm2408m (LEP)21700tail
Fenix SD111000lm45m18650rotating ring
Acebeam D202700lm296m21700side switch
Nitecore DL201000lm223m186502 side switches
Dive lights from reputable brands



  • Very waterproof
  • Rotating switch is intuitive and well designed
  • Beam profile works well underwater
  • Stays on high as long as the cell can provide power
  • Comes with cell and charger


  • 300lm low isn’t very low
  • 6000K LED is too cool for my liking

Subjective changes and improvements

Firstly, I’d have called this light the SD05B to differentiate it from the version with the step down.

The rotating switch could do with more knurling for grip. I don’t know how this would affect things for divers but it’d make using the light a bit easier for me.

The cool white XHP50.2 is the brightest 3V LED you can get but I’d be happy to sacrifice a few lumens for better light quality. A high CRI 4000K SST40 emitter would work well here. I’m not sure what effect this would have when diving though.

I’d like to see a slightly smaller EDC version of this light that only takes 18650 cells, has a smaller head and comes with a clip. To make it more useful for every day use it could do with 2 lower modes, around 1lm and 50lm.


The Sofirn SD05 was more fun than I expected – I’m now checking the IP rating of all my other lights to see if they can be used in water. The SD05’s quality is great and I have no doubt that this would be a solid light for actual diving. Sofirn listening to user feedback and updating the light is a great sign.

Thanks to Sofirn for providing the light for review.

Join the Conversation


  1. Over a year this was originally posted, so my facts are from memory.
    The SD05 is marketed as a scuba diving flashlight and the original version with a timed step-down is non-sensical. It is not designed as an air-cooled device. Sofirn’s take is an afterthought that made the light useless in diving. However, it had a constant current driver that maintained its output for the 3 minutes.
    The second version is ATR (Advanced Temperature Regulation) and so they felt it could handle the higher lumen output, alas it drops as time passages. Again, almost useless in diving as the temperature sensor is within the MCU and reacts to the board’s temperature and not necessarily to the environment.
    I needed a weatherproof light that is reliable and sustains its output in some extreme conditions – -40ºC with wind chill and blizzard conditions. The first version drops and I lower/up the mode for another 3 minutes. The 2nd version doesn’t respond to such and just continues to drop. Got to vigorously shake the thing in the wind to have it cool down. And then there is the fact the user will have gloves – I can’t feel the heat other than passing close to my face.
    Sofirn’s conservative approach is lacklustre in my opinion. It’s unfortunate for the design and ring control are very nicely implemented, as the thicker lens and the 21700 cell choice.


    1. > Again, almost useless in diving as the temperature sensor is withir the MCU and reacts to the board’s temperature and not necessarily to the environment.

      I think you’re right about the temperature sensor being in the MCU. When doing a run time in water it sustained lumens significantly better than in air on the high mode. From what I can tell it’s working to an extent in the water, where convection keeps the while light cool.

      I’ve never been in -40⁰C temperatures but I guess if there’s little wind then the main way heat will dissipate is with radiation, which won’t be quick.

      There may be a way to disable thermal regulation but that could be dangerous.


  2. When diving, cannot the water/cold environment cool dow the flashlight to keep it burn at the turbo mode?


      1. I’ve had it submerged for a few hours at between 1m and 2m with no issue. I haven’t tested it down to 100m.


  3. Good review generally but would be great if it is tested as a dive flashlights.

    Just to add:
    Magnetic switch is important for dive flashlights due to pressure. Normal button switch may not be practical (as it may not be able to be pushed to off.)
    The rings are important to keep the water pressure from seeping in.
    At 50m depth, natural lights cannot be reached and some spectrum of lights are lost. You may not be able to see anything red in colour, therefore it is good to have 6000k lights to compensate the lost spectrum.
    Temperature of the flashlight is important to avoid “killing” micro/small swimming friends


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