Recreational divers use underwater lighting equipment for two simple purposes: to see with or be seen by. In this article we will review the different situations divers find themselves in that benefit from or require artificial illumination - from shallow water day diving, to deep water wreck penetration. We'll look in detail at lighting options from simple chemical lights to high-intensity exploration lamps. We will also offer advice on how to power, maintain and carry underwater lights; and provide guidelines on safe diving practices to help you plan safe light-dependant dives such as at night or in overhead environments. We hope that this guide will help you to choose the lighting system that will best match your own personal diving scenarios. Beginning divers usually make their first dives in relatively shallow and bright conditions. In such favourable situations a dive light may seem unnecessary.In fact a small torch may prove very useful and can greatly enhance early experiences. Using a torch will let you see truer colours such as reds and oranges. The underwater world is a very vibrant one, of spectral shades and hues. Look at a wall matted in muddy brown fuzz, shine a light on it and you'll discover reds and oranges that seem to fluoresce. These colours define the animals that colonise the rocks and give shape and texture to them. Colour also reveals the identities and even the moods of fish, yet many divers only look in monochrome. A torch will put the colour back and moving from rock to rock and discovering the true colours of plants, animals and fish can rapidly become addictive. Many marine animals, particularly solitary ones who lack the law of averages protection offered by shoaling, are vulnerable to attack out in the open. The diver who investigates undercuts, overhangs and holes in wrecks and reefs will find a wealth of marine life including predators such as eels and octopus that are fugitives by day. For this type of use a small two to four cell light is all you need. A narrow beam penetrates bright sunlit water best for revealing true colours up close and is ideal for aiming into holes. It can be kept in a pocket until needed, hung from your wrist or pressure gauge or clipped into a holster on your leg, arm or belt until needed. Many popular diving activities require lights in order to see. Examples include diving deep, darkwater diving in poorly lit areas like quarries, cave diving, night diving and wreck penetration.

For this type of activity where there is, to all intents and purposes, no natural light the diver's lamp becomes an essential item of safety equipment. Large wide beam lamps, powered by at least four D-size batteries, or a single lantern cell, are usually used as these provide a wide enough beam for the diver to be able to see his surroundings. Since the diver may have to pick and weave his way through a cave constriction, companionway or reef, it is vital that he can see a large enough area well enough to plan his route. A small light with its narrow pencil-beam simply does not reveal a diver's surroundings adequately and will slow the diver down as he shines the light about him to try and get a disjointed impression of where he actually is in relation to any hazards - hazards that might cut, entangle, fall in on top of him or block his path. If safety is achieved by being informed then you need to see the whole picture in order to assess risk and minimise it.

How much power do you need? It's difficult to be specific. Light manufacturers use outputs measured in lumens, candlepower or watts to describe how bright their lights are. This makes it difficult to do direct comparisons between different models. Since light falls off as a square it is an issue further complicated by how wide the beam is. Again beam width is not standardised. A small day diving torch can be as bright as a wide beam powerhouse because it's output is concentrated over such a small area. Additionally, taking the light underwater in even the clearest conditions will probably halve it's output through absorption, diffusion and scatter. Output needs also vary with the activity. In low vis. a high power light may actually reduce how well you can see through reflection off particles in the water, or may be so bright that it causes some instrument displays to 'disappear'. On the other hand, in reasonable visibility a powerful light will let you see much more, making your diving activities more enjoyable and probably safer. As no single light will meet all the requirements of the typical diver and most divers make dives that, for safety reasons require a back up to be carried, it follows that most divers will end up owning more than one torch. Thus, they can select lights that provide optimum lighting for specific situations with a degree of overlap. It helps to think about the type of diving activities you do or plan to do and build a lighting system to match those requirements rather than choose equipment in isolation.

As a rough guide to useable outputs I would suggest the following:

day diving lights only

3 watts

day diving lights that will also be used as back up lights for night, darkwater, wreck, cave or cavern diving

5 watts

primary light for night, darkwater, wreck, cave or cavern diving

8 watts

underwater video lights

50 watts

For back up, primary and video lights these are minimum output recommendations.

Amongst European recreational divers and divers making technical-level dives, lights putting out from 50 watts are common. We are slowly seeing an increase in the number of British sport divers taking advantage of this kind of advanced equipment.

Apart from lights to see by, many divers also use lights to mark their position so that they can be easily seen by other divers or surface crew.

Chemical lights have long been popular for this. A plastic tube containing a chemical encloses a glass phial containing another chemical. Bending the light stick and shaking it causes the glass tube to break, allowing the two chemicals to react and emit a glow. The glow is adequate to indicate a diver's position. As various colours are available, divers can be colour coded to identify individuals such as the diveleader. Chemical lights are single-use devices which work for anything from minutes to hours and once exhausted cannot be reactivated. They are expensive to use if you need markers regularly and if you have a dud you won't know until you try to activate it.

An alternative is to use a marker torch. These small, low power lights use a filtered cone to provide a soft glow that can be seen from almost any angle. They can be reused and tested like any dive light and will be cheaper to use for those divers routinely needing markers.

Strobes are flashing beacons used by many divers. They are often very high powered (some use components from camera flashguns), and are easily visible over great distances on the surface. Underwater they are not only used to mark divers but also to mark anchor or shotlines to aid divers in relocating their ascent point.

Markers need to be mounted where they can be easily seen by a diving partner underwater or people on the surface. Common places are snorkels, mask straps, tank valves or the shoulders of BCDs. These locations raise the strobe above the water level when the diver is on the surface.

Dive lights are made up of five main components. Understanding a little about the options you will be offered in terms of bulbs, reflectors, switches, grips and power packs will help you to choose your dive light(s) intelligently, and ensure you get the system that will meet your own particular requirements best. Lights can be turned on or off using a variety of switching mechanisms. Some lights require you to simply screw the front of the torch in and out to operate the light. These switches are simple and quite reliable. The o-ring can breach if, for example, the light is dragged through silt during a dive and the threads become clogged. They can also flood if the user turns the switch in the wrong direction, unscrewing it from the torch body. Turning the light on and then off by a quarter turn can help prevent this - if you turn the switch more than a quarter turn and the light hasn't come on, you're turning it the wrong way. Switch locks are not usually uttered with these lights which are unlikely to turn on accidentally. This type of switch can be difficult to operate one-handed.

Direct switches use a simple lever and through-case control shaft sealed by an o-ring. Like any o-ring it can become worn, displaced or perish and leak. However this is unusual and the o-ring is usually easy to get at for servicing either by the owner or the dive shop. One-handed operation is normal, though switches with safety locks to prevent accidental operation may need both hands to unlock and turn on.

Toggle switches are similar in principle, but the on/off lever is covered by a waterproof boot. Leakage can occur if the boot is torn or perishes. They are usually easy to use single handedly. Switch locks aren't normally offered.

Magnetic switches require no penetrations in the torch body. A switch on the outside of the light uses a magnet to open and close the torch circuits on the inside. This type of switch cannot leak, though they can still fail mechanically. They provide for one handed operation as a rule, and often incorporate a locking mechanism.

A switch lock is built into some lights to prevent the light turning on inadvertently, especially while it is in your gear bag. Not only will this run down your batteries but the heat may cause some lights that are designed for underwater use only to be destroyed. Reversing the battery pack supplied with some lights can also prevent a light turning on. Narrow beam lights, such as day diving lights designed for looking into holes, usually utilise smooth reflectors to concentrate the beam. These are often termed spot reflectors.

Medium beam torches represent a compromise between very small daylight only lights and the much larger wide beam lanterns. They make excellent general purpose and back-up lights. They usually use dimpled reflectors.

Wide beam lights used to illuminate large areas for activities like night or wreck diving normally use dimpled reflectors to spread the beam. These are often called flood reflectors.

Video lamps use high quality wide angle reflectors to provide intense, even illumination to match modern video camcorder lenses without causing hot spots. The beam spread is far wider than a conventional wide beam dive light.

Some manufacturers offer a choice of interchangeable spot and flood reflectors to meet different needs. Normally these are user changeable.

Lights are most effective when the beam is properly focused to provide an even beam without distracting hot spots and dark patches. Some lights use factory prefocused bulbs and reflectors which do not require user adjustment. Others may need to be focused by adjusting the position of the bulb before the torch is sealed. Lights may also be adjustable during the dive and this feature can be enhanced to permit the beam to be varied between spot and flood during the dive to suit the diver's lighting needs of the moment. Dual filament bulbs sometimes provide this feature by using one filament for spot and one for flood settings, selected via a three position switch.

Bulbs for dive lights are usually designed to provide a white beam which reveals truer colours and penetrates further underwater. Gases are added to the bulb to increase performance. Halogens are used in many high performance lights. Krypton or argon may be used to reduce cost but will not be quite as bright.

Dual filament bulbs provide an instant back-up in case one filament fails. By flicking a switch you can bring it into immediate use. This can allow you to continue your dive but does not obviate the need for a back up - a flooding or battery failure will render both filaments useless. Dual filament bulbs sometimes offer a choice of high and low power settings. The low power filament usually has a longer lifetime.

Small lights usually fit the hand easily and don't require separate grips. Large lights often have pistol or lantern grips. If you plan to dive in overhead environments or use a distance line you should consider a grip that allows you to hold the light and a purpose designed penetration reel in the same hand. Negatively buoyant lights are preferable as they can be set down on the bottom beside you. Also, a light that floats away from you when you need it isn't helpful. If you do drop a light you are more likely to able to find it again if it stays on the seabed than if it floats away on the currents. Floating lights can often be weighted to make them negative. Some divers use neoprene covers to make their lights positive at the surface and negative at depth where pressure compresses the neoprene. Doing so means that they can lay the light down on the bottom, perhaps to illuminate something they need both hands to examine, but that if the light is dropped when they hand it up to the boat it won't sink and be lost. It's important to think about how you will carry your lights so that they are easy to deploy, but do not get in your way when you aren't using them. Your lights need to be rigged so as to avoid interfering with other equipment, encouraging entanglement or detracting from your ability to manage a problem. If you choose to hang your light from a wrist lanyard it should have an elasticated section to allow you to drop the light quickly, if for example you need to buddy breathe when a swinging dive light could get caught up around your regulator. If you will be carrying other items on the same wrist such as cameras or collection bags, think about which items it will be most useful to release first and put those on last.

Small lights can be placed in BCD pockets. Longer torches can sometimes be stored in the gussets located behind the pockets on some jackets. As a light can fall out because of a pocket flap coming adrift or because it can be tricky to replace a light correctly in its pocket when you can neither see nor feel what you are doing properly, also use a clip to secure your torch to a jacket D-ring to avoid losses.

Slimline torches can often be snapped into dedicated holsters which can be belt, leg or arm mounted. Some divers use arm mounts to provide in-line, hands free illumination. Underwater photographers utilise holsters to attach small torches to their flashguns to help with strobe aiming and focusing with SLR cameras. Divers who have graduated to the larger exploration lamps can also use these holsters to attach back-up torches to their main lamps. This can be the most convenient place since large lights can be an encumberance should they fail or run down unexpectedly because of their bulk. Rather than trying to manage a large lamp while simultaneously fumbling for a back up the diver simply turns on the back up attached to the main light

Another option is head mounting. This leaves the hands free for operating tools, laying lines or assisting another diver. However, reflected backscatter usually mars performance over anything but short distances. Some divers use low power head lights for reading instruments in low light. Head mounting is achieved using mask strap connectors, attachments to the mask frame itself or by wearing a helmet. Head mounting is a viable place to locate a back-up light since it is fixed in position and consequently swift to operate. A hazard created by head mounting is that when you look at your buddy you tend to blind him.

Video and exploration lamps sometimes use separate battery packs cabled to a light head. This provides for long burn times at high output and places the majority of the bulk and weight of the unit (the power pack) out of the way. A very small lamp head can then be used, minimising drag and making it easier to deploy a reel, for instance. Divers using this type of system for shooting video with the light heads attached to the camera housing and the battery pack to themselves may want to use quick release cable connectors to avoid being tied to the camera in an emergency. The power packs can be waistbelt mounted, attached to the side or back of a cylinder set or fastened to the base of a set of doubles. Camera people can sometimes attach the pack to the base of the housing.

If a light is to be clipped to the diver then snap hooks should be avoided. They can clip themselves onto shotlines or into cables around wrecks. Particularly in confined spaces encountered in penetration diving, it can be very hard to locate and release by a diver using gloves who probably won't even be able to actually see the mechanism. Piston clips are preferable. They should be mounted on the accessory and snapped onto a D-ring on the diver - not the other way round. Fastex clips as used on BCD releases and on fin straps are another useful way of securing lights.

Cave and cavern divers need to avoid becoming entangled in their guide line which is usually laid out below them. As dangling lights could easily foul the line, some divers clip their back-up lights to their tank bands. By crossing over the guideline backmounted equipment is kept clear of it and foul ups are avoided.

Excepting chemical lights, recreational dive lights all use batteries for power. Professional divers and filmmakers needing very high intensity lighting for any length of time use lamp heads run via umbilicals to surface generators. This gives them more or less unlimited burn time at thousands of watts, compared to a top output in diver-carried lights of around 800 watts for 20 minutes.

Disposable alkaline batteries work well for occasional torch users. They are cheap to buy, usually provide hours of burn time and do not require the care and attention that rechargeable batteries do. Travelers can usually buy them abroad and can dispense with the weight and bulk of battery packs and chargers. Because alkaline batteries die slowly they should be used in back up lights - rechargeable lights sometimes provide only a few seconds warning between working at full power and going out. Obviously if your main light has just failed you don't want to turn on your back up to find out that a problem battery is going to immediately knock that out to.

Regular torch users will find rechargeable lights more expensive to buy, but much less costly to run. Most lights use nickel-cadmium cells. Looked after they can be reused 500 to 1000 times. With some NiCads memory can be a problem. If the light is partially run down, say run for twenty minutes instead of used for its rated burn time of perhaps ninety minutes the batteries may eventually develop a memory and may only run for twenty minutes subsequently. Usually the memory can be corrected by running the light until it starts to dim and recharging it fully a few times.

Gel cells are used in a few lanterns. They are rechargeable 100 to 200 times. Unlike NiCads which work at full output for almost all of their charge, then die with little warning. Gel cell powered dive lights dim more slowly, giving the diver more warning that they are running down. They can have similar memory problems to NiCads.

It is best to turn any rechargeable dive light off as soon as the light starts to fade rechargeableor the beam colour starts to turn yellow. Deep-discharging the batteries will damage them. Follow the light manufacturer's instructions to get maximum life and value for money from your batteries.

If you choose a rechargable light it is worth considering a few points. For example will you have enough burn time? A diver making deep dives will usually have so little bottom time that a 50 watt exploration light which only lasts for 25 minutes will meet his requirements for high output for illuminating a wide area. A diver making long night dives in shallow water will need a much longer burn time - possibly over an hour and will probably have to sacrifice brightness for duration. Repetitive diving brings further compromises. Few lights last more than 90 minutes and not only may this not be sufficient for a day's repetitive diving, there may not be a long enough surface interval between a night dive and a dive the following morning to recharge. Typically dive lights take 12 to 14 hours to fully recharge. With some lights the solution may be to carry extra power packs so that one can be kept on charge while the other is in use or some manufacturers can supply a fast charger to bring recharge times down to 2 to 4 hours. Alternatively it may be possible to use disposable batteries. Think about where you will have to recharge. Regular dive lights are usually supplied with a 240 volt charger. Abroad and on live aboard boats 110 V is common. You'll need a transformer and probably some plug adapters. Exploration and video lights are usually provided with dual voltage chargers. If there simply isn't a mains supply or a generator you may have to investigate using car charging adapters or solar chargers.

If all your diving takes place in well lit conditions and a torch is just used to look into nooks and crannies and to reveal true colours a light failure is merely irritating. If you need a light in order to see, because for example, you are exploring inside a wreck, then a light failure might cause you to die. This section is intended to explain principle causes and effects of dive light failure in these circumstances and to offer advice on how to stay safe.

It is stressed that anyone making light dependant dives should be formally trained in appropriate specialised techniques before undertaking such dives. Light dependant dives include overhead environment diving such as wreck penetration, cavern and cave diving. Remember that when you compromise your safety you also compromise your buddy's safety as well as that of any third party rescuers.

Dive lights can fail for many reasons. Examples include being knocked about which can cause bulbs to break or batteries to slip out of alignment. A bulb can wear out. An o-ring can fail and flood the light. A battery may be faulty. A light can be lost. More likely, the user will have made a mistake. Perhaps the batteries weren't replaced or rechargeables haven't been properly charged or maintained. Carelessness in sealing the light might mean that a damaged o-ring was overlooked or out of alignment.

Lights usually continue to work for some time after they flood and will probably provide enough time and light for a diver to surface from a typical recreational dive. Mechanical problems tend to kill the light immediately. The effect of a total light failure will be to plunge the diver into near or often total darkness. At best he may be able to see by the light of his buddy's torch. A penetration diver who has laid a guideline may be able to retrace his route to safety in total darkness but it will take longer, particularly if he has to negotiate tie-offs and wraps. Any additional time taken will deplete air supplies and increase decompression time.

Use multiple lights. Cave divers operate in environments with no natural light. It is their standard practice to carry a minimum of three lights each. Cavern divers who dive in sight of natural light at all times use a minimum of two lights. Back-up lights need to be bright enough to enable you to get out of whatever you've gotten into. That implies a quality light with reasonable output.

Ensure that each of your lights has a burn time that is sufficient to get you to safety with a large safety margin. A delay for whatever reason could cause a light to run down if you don't make allowances - just as you would for air duration. I use an exploration lamp for night diving which has a burn time of 45 minutes at 150 watts. Because I can expect this light to run down before I want to finish my dive (usually lasting 90 minutes), I don't figure this light into my planning. Instead, I carry two other lights, one for use as a primary when my gloom buster fails and another to back up the primary. Either of these lights provides duration way in excess of the time I plan to be underwater. If I am running a night dive for students I make sure each student has a primary and a back up light and I carry another spare that can be used by anyone on the team as a primary if they have a light failure. This is done to avoid having to abort the dive if a light fails - back up lights are escape lights: if your primary fails you use your back up to surface not to continue the dive!

Divers often buy dive lights early on in their careers and give selection little thought - just as I did as a beginner. In reality choosing a lighting system requires a little research and some care. As my experience grew and the diving activities I participated in changed, so too did my lighting requirements. Now my armoury includes lights with outputs from 5 watts to 250 W. Hopefully this article will help you to get your selection right from the start and avoid the costly pitfalls I fell into.