[Review] Sofirn SD03

Sofirn approached me for a review on their new 18650 SD03 diving light. I’m not a diver, and especially can’t test its IP-rating to depths of 100 meters. However, it survived for an hour in our rain water tank (approx. 1.5 m). So, this is not a fit-for-purpose test, but I’ll give an overview about the main features of this light.

Scope of delivery and specifications

The cardboard box contains the light, spare o-rings, a lanyard and a charger. The manual is missing, but you’ll find all the information here.


The specs according to the manual:

  • Luminus SFT40 at 5000K
  • 18650 battery, 3000 mAh
  • Working Voltage: 3.0V-4.2V
  • Magnetic E-switch
  • AL6061-T6 aluminium alloy
  • Water Resistance IP68 (100 m)
  • Size: 34 mm (head diameter) * 126 mm (length)
  • Weight: 102 g (without battery)
  • Reverse polarity protection
  • Advanced Temperature Regulation (ATR) technology: In Medium or High mode, the flashlight heats up easily. To prevent overheating, the SD03 automatically reduces the current output when the temperature reaches 60 degrees.
  • Low Voltage Warning: The SD03 automatically drops to a lower brightness level when the battery voltage is lower than 3.0V. When it drops to Low mode, the main light flashes twice one minute apart, indicating that the remaining battery power is poor.
  • Modes: 300 lm (198 m/4 h), 1000 lm (331 m/3 h), 1800 lm (447 m/1h30 uncooled/55 min cooled)


Sofirn used to use a magnetic control ring for the modes/off in their diving lights, but on the SD03 there’s just a spring loaded switch. I know this already from Wurkkos diving lights and it works well, though there’s no haptic feedback. Already known from the also new SD06 is a new mechanism for locking/unlocking the light. The switch can be turned 90 degrees to disable itself.

This means you cannot only prevent the light from switching modes and turning it on, but also from turning it off! Since the knob is quite small, operating it is a bit fiddly, but works with bare fingers.

Single press turns the light on, successive presses switch through the three modes, and a long press turns it off. There’s mode memory and no blinkies.


The SFT40 is a domeless LED and sits beneath a rather deep reflector. The light quality at Ra 65 is moderate, the spot is slightly green.

The beam and spill are pretty tight, as expected from such a setup. A range of 447m is a lot for a light this small. There’s a ring around the beam.


Some grip is given through the bulges, there’s no way to mount the light on a rig, but a strap can be attached to the tailcap. However, the carabiner hook doesn’t attach to the light, but maybe I’m doing it wrong.

Sealing is done with two o-rings (a set of spares is provided), the bezel is apparently glued and there’s no tailcap.

The thread seems to be square cut(?)

Runtime High, ATR and LVP

After the runtime measurements, the light went out and the battery was at slightly over 2.9 V. I have not catched the time span where the light blinks to indicate low voltage. The light spends most of its runtime in High mode at about 700 lm (uncooled), which is not bad, but also not best in class for a regulated 18650 light. Anyway, this beats unregulated lights easily.

I don’t understand the ATR, which is in effect for about 50 minutes and causes the light to ramp up and down, each for about 25 minutes.


This is a very simple light in terms of the UI. I dislike memory mode, but with only three relatively bright modes it doesn’t matter too much. The locking mechanism is nice, though I’d have preferred a magnetic control ring instead of the magnetic switch. There are no blinkie modes.

The modes (300/1000/1800) are not evenly spaced, and the lowest mode is quite bright. This might make sense for divers, keep in mind this is certainly not an EDC light where you’d want some lower modes, so no critics here.

From the casing, I’m confident the light will survive quite a depth, but have checked watertightness at only 1.5 meter.

I like the regulated output very much, but the ATR, while working, operates pretty strangely. The body and especially the threading is nice.

On Ali Express, the SD03 costs a bit over 30 Euros, on sofirnlight.com it isn’t available yet. So, it’s dead cheap and has some nice features. As a diver I’d consider it a backup light, or, in shallow waters, a fun gadget not really needed.

I hate being so wrong - the bezel can be loosen with some force. It is also sealed with two o-rings :slight_smile:

So, you can have this light with little effort in HCRI and warm light:

Could it be the same new driver as in Wurkkos FC11C and possibly in Sofirn HS42?

Difficult to measure the currents since the battery is loaded from the head (no tail cap). If anyone has a good tip how to do it, I’ll try.

Wow nice review. Do you like our new switch comparing with the old one?

1 Thank

Thank you!

The locking mechanism is a novelty, so it’s interesting. In addition, the chance to accidentally activate the light ist extremely close to zero. Overall, it does a good job. I guess it is a good choice for a diving light. However, I generally like magnetic control rings better, but that’s just a matter of personal taste.

So glad to hear that :blush: