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Title says it all really. I am looking to buy a diving torch as I am taking up diving next year.

What am I looking for? They seem to range from 100lm to 2500lm. Realistically how many lumens are actually needed to effectively see in murky water? (I live in the UK so the water will be equivalent to soup.)

As an additional, what is a required battery life for a diving torch? Some only last 30 minutes which, to me, seems too low.

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This is not an easy question to answer. More lumens means better light, normally also further range. But if you dive in areas with lots of suspended particles in the water you will get a lot of back scatter which in effect impacts on visibility.

Then the next question is do you need it for night dives or just to help see more colours on deeper dives where your colours have become dull and especially red has disappeared?

The best option for a dive light is:

  1. Batteries lasts at least 25% - 50% longer than your average dive time
  2. It uses standard batteries (AA, C or D) and rechargeable versions of standard batteries
  3. It uses LED lights (less power usage for more lumen and light tends to be white rather than yellow)
  4. Adjustable Strength - some dive lights have 2 or 3 settings so you can increase/decrease power as you need it
  5. Narrow beam, better to focus on what you are looking at

I would say you would be good with about 200 - 500 lumens. Also you will go for a very strong light as primary and then a smaller light for backup in case of major issues on a night dive.

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  • I'm guessing that the solution to backscatter is the same as for fog in the air? Namely, to move the illumination further from one's eyes, so it's shining somewhat across the field of view. I'm not a diver, so don't know if this translates (water droplets have a very strong reflection straight back like cat's eyes, but I guess the particles in water don't so much). Nov 26 at 10:59
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Lumens is the amount of light emitted from your torch. If the same amount light is spread in a tight beam, say 6 degrees, it will appear much brighter than the same amount of light spread over a wider beam, e.g. a 12 degree beam is about 4 times the area than a 6 degree beam, so will appear to be less bright.

The big issue is the type of conditions you dive in. If there's a lot of sediment in the water, as is normal for UK diving, then you'll find a wide beam produces a lot of back-scatter, whereas a tighter beam will produce less. It's like driving though fog where it's best to use a dipped beam than full beam.

Being slightly cynical, there's Lumens and there's Lumens. A lot of the cheap and nasty far-eastern torches will claim enormous amounts of Lumens; quite frankly many appear to be made up numbers. Also cheap torches are a waste of money; they break after a few usages and literally dissolve in the water. There's nothing worse than discovering your torch won't work when you need it.

The best torches are heavy-duty with decent sized batteries. These are normally umbilical meaning a thick cable connects the torch head in your hand to the battery on your waist belt. The torch head usually has a "Goodman handle" which effectively frees your hand with the torch head on the back of your hand. Needless to say umbilical torches are expensive >$500, but they're very reliable and have several hours of battery life. My primary torch is a Light-For-Me 4Tec which has 1200 Lumens in a 6 degree beam pattern and a battery life of over 5 hours -- easily enough for a weekend. Other similar torches are available, all are excellent and reliable.

Smaller backup torches tend to use the "screw" head to turn them on and use standard non-rechargable batteries. This is because rechargable batteries discharge over time; you don't want to discover this when your main torch has failed. You did check your torch before you dived in?!? Backup torches are normally stowed on your chest harness, below your D-ring. If diving in an overhead environment you always take at least two backup torches and one primary torch. Typically they'll have a tight beam and be of the order of a few hundred Lumens. My 3 x AA battery backup torches (Ammonite LED1) last for a couple of hours; easily enough to last the rest of a dive.

Another benefit of a tight beam pattern is for signalling. You can communicate using "passive signalling" to your buddy where you are: typically if your buddy is in front of you, your beam will be pointing just in front of them so they can see you're keeping up. You use active signalling to get their attention, or rapidly waving the torch beam around to immediately get their attention in emergency.

Recreational torches tend to have wider beam patterns, so need a much greater light output. This means that to be small they have a short battery life at full power. They can easily cost the same as a fully-featured technical umbilical torch with many hours of battery life.

The other type of torch is a video torch. If you're taking photos, you'll need a very wide beam spread, so you'll need an enormous light output spread across the beam to light up the target. These can be eye-wateringly expensive, easily >$1000.

So lots of choices.

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No amount of lumens will allow you to effectively see in very murky water. If water visibility is about 1m, you won't see more than 1m no matter if you have 500 lm or 5000 lm. A very strong light will make a difference between dark soup and a soup that blinds you. However, a decent light will make you visible from a bigger distance. If you see a dark soup being light-green in some direction, you know a diver is somewhere there.

However, a bit deeper when a water gets less murky, 100 lm is more a positional light as a light that will let you observe the vicinity. With my 1000 lm I see good in about 3 m, but to see further, I need a light from my buddies, who have stronger lights. From my experience, 1000 lm is an absolute minimum in the lake.

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A diving light is an essential piece of equipment that divers should bring with them on every dive. A dive light gives colour to a blue environment, whether you're diving in murky or clear water, at night or during the day. However, around 20-30 feet below, experienced divers notice that everything becomes dull during the day.

Depending on your needs or the type of diving you wish to do, any light with an average beam angle of 12 degrees to 75 degrees and a lumen output of 200 or higher should be adequate for recreational diving. For safety, night divers should have both a main and secondary diving light. Choose a light with a wide, brilliant beam that can pierce the darkness for the best visibility in nighttime seas. The usual guideline for dive lighting is that the brighter, the better.

BESTSUN dive flashlight has two 18650 lithium rechargeable batteries and an extended standby time. When diving, the maximal brightness is up to 10000 lumens, and the 8 degrees super perfect spotlight, the white light of 6500K, shows the actual colour of the surrounding environment.

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