The Design
The Sub M3 is a small hand-held dive-lamp that uses three high-output LEDs and highly polished reflectors to provide a smooth spot beam. It is powered by lithium-ion batteries permanently sealed in a marine-grade anodised aluminium housing that’s depth-rated to 200m.
What makes this light stand out from the crowd is its switching mechanism or, to be more precise, the lack of it. It’s totally switchless......

The concept behind the Sub M3 is Exposure Marine’s pioneering Motion Control Technology (MCT). A simple clockwise or anti-clockwise movement pattern will lock, unlock, turn on, turn off and change power modes. Give it a few taps and it will enter an SOS Flashing mode too.
The light is designed to be worn on the back of your hand, using a neoprene mount, giving a truly hands-free operation.
A rotation-sensitive digital fuel gauge, displaying remaining burntimes in hours and minutes, is set behind a clear Plexiglass panel at the rear, and also serves to indicate Power and Travel Lock modes as well as a charging gauge showing the battery’s fill level as a percentage.
The light is charged via a clever dual wall-charger with a USB option. Two gold-plated wet connections and a magnet to hold the lead in place complete what is a well-thought-out product.

In Use
When I showed the light to some of my friends at Wraysbury Dive Centre, they were sceptical at first, and concerned that the circular movement required to operate the lamp would look too much like the “Are you OK?” sign, the training-agency standard gesture used on night dives.
A good point, but in practice the unit required a very small circle of movement to do what I wanted it to do.
It is unlocked from the Travel mode by holding it vertically and scribing a small clockwise circle, then you hold it horizontally and scribe another clockwise circle to turn it on.
The light has two power modes, High and Low, and switching between them requires more small circular movements – clockwise to power up and the reverse for down.
With the light on and held vertically downwards, tapping the body switches it into the SOS Flashing mode. It is switched back to a normal beam when a horizontal circle is scribed.
I know this all sounds incredibly complicated, but after a little practice it’s a walk in the park, and quickly became intuitive for me.
I enjoyed the freedom of not having to reach round to find buttons or switches, especially while wearing thick neoprene gloves.
The one-handed operation meant that I could concentrate on diving as opposed to adding to the task-loading.
On the High setting the light is very bright. The narrow beam cut through the poor visibility like a knife through butter. I prefer this to a wide or flood beam in these conditions, as it doesn’t illuminate so many suspended particles and have a reverse effect, akin to driving in fog with your main beam on.
I found the Low power setting a little on the dull side under water in daylight, but in a dark environment it proved more than adequate for navigation and instrument-reading.

Bucket Test
As is becoming common practice at the DIVER Test Centre, I fully charged the light, switched it onto full power and chucked it into my yellow bucket of water to test the actual burntimes.
On full power it lasted for 126 minutes – six over the maker’s stated two hours.
The battery gauge looked to be very accurate as it timed down.
I fell asleep during the low power test – forgive me, but 18 hours is a long time to stare at a glowing bucket and a timer.
In between tests the light took just short of 12 hours to fully recharge. The battery gauge has only two digits, so 99% is all you’ll get to see when it’s actually full.

Cupping Support
It became apparent that the hand-cradle needs some modification. It holds the lamp at a slightly downward angle and has just one Allen head bolt at the front to mount the light.
When I used the Sub M3 in real-world conditions it worked loose quite quickly and started to swing on its axis. I contacted the guys at Exposure Marine, who told me that they would find a solution and modification.
Although not very elegant, a cable-tie sorted the problem out for me while on site.
Exposure Marine tells me that it has since modified the cradle on the wrist-mount to increase the stability of the light and reduce the risk of knocking it out of line.
The new cupping support (pictured above) will feature on future wrist-mounts supplied for the Sub M3. Existing owners can get in touch for a replacement (at

The gazillion dive-lights available all have claims to be brighter, last longer, go deeper, weigh less or be smaller than its competitors, but Exposure Marine’s Sub M3 with its MCT is very different.
The build quality is excellent and it works very well. My initial scepticism soon turned to admiration for a product that can do it's job with one hand tied behind its back.

BEAM 20° Smooth Spot
OUTPUT High 1563 lumens, Low 282l
BURNTIMES High 2hr, Low 18hr
SIZE 116mm x 53mm
COLOURS Black, orange or red
DIVER GUIDE width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100%