# How many lumens for a diving torch?

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.

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.

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 descent 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.