So, you’ve just been diving with someone who’s got a great torch. It lights up even the darkest corner of a wreck or can illuminate a wrasse (other fish are available, apparently) from 5 miles away. You’ve got torch envy, but you don’t know a 10w HID from a 50w halogen, fear not though, this article aims to help
Types of Torch
The two most fundamental types of dive light are conventional self-contained lights and umbilical or canister lights
Conventional Self-Contained Lights
Conventional self-contained lights are what people often buy as their first light. The light is a single unit, the body of which is typically made of plastic, which contains the batteries, switch, lens, reflector and bulb. They come in many different sizes and configurations. The most common configurations being hand held (i.e. the torch is sufficiently small to fit in the palm of your hand, think of a normal flash light), pistol grip (the torch has an angled handle built off the bottom, see Underwater Kineticsâ€™ bigger lights) and carry handle (the torch has a handle built parallel to the top of the torch, see Kowalski). The main benefits of conventional style lights are that they’re simple and hence there’s less to flood or go wrong, they’re generally quite tough and they’re at the cheaper end of the market.
Prices for conventional torches range from under £10 to over £300
Umbilical lights are the more serious end of the market. They comprise a canister (or â€œcanâ€) which contains the batteries and switch, and a light head which contains the bulb, reflector and lens. The two parts are connected by a cable. The benefits of canister lights are that they allow you to have plenty of space for batteries while keeping the part you hold small enough to mount of the back of your hand (using a device called a Goodman handle) which leaves both of your hands free to do other things, they also allow the batteries (which generally don’t like to get too hot) to be kept away from the bulb (which can get very hot). Additionally, because the battery packs can be larger, not only do they give you more power, they also weigh more, meaning less weight on your weightbelt.
Prices for umbilical light systems generally start around £250 and go to over £1000
There are 3 main choices for bulbs: HID, Halogen or LED.
HID is great. It gives a distinctive, clean bluish light and uses arguably the least amount of power for a given amount of light output and length of time. Predictably, itâ€™s also by far and away the most expensive of the three options. The bulbs are expensive (commonly over Â£100), fragile, near impossible to get hold of locally and comparatively short lived. HID bulbs also need a dedicated circuit called a ballast to power them that adds complexity to the light. HID bulbs are not often seen outside of umbilical systems.
Halogen is the classic choice. Halogen bulbs are available in a wide range of outputs from a fairly large number of sources (maplins stock them in a wide range of styles) and at very moderate cost (a few pounds). The bulbs are still fragile, but less so than HID and they’re sufficiently cheap that you can carry a spare or two. The biggest downside to halogen bulbs are their prolific appetite for battery power: for a given light output, halogen bulbs typically use 5 times more power than HID. They also have a rather pink light underwater (as standard). They don’t require any special circuitry either which reduces costs still further.
The newest option is LED, which is gradually becoming more popular and looks set to continue to do so as the technology advances further. LED â€œbulbsâ€ vary massively in cost: from the LEDs that most people are familiar with, which cost a few pence but offer, at best, rather puny light output; to 20 watt monsters costing about £40. The biggest benefits with LEDs are that they last almost indefinitely (provided the torch is designed right), produce a crisp, blue light, similar to HID and are fairly resistant to being knocked about. LEDs efficiency is somewhat debateable, but itâ€™s generally considered to be somewhere approaching that of HID. LEDs require special electronics to get the best from them, but these circuits are cheap compared to HID ballasts and less fragile. It’s more difficult to focus LEDs compared to the other two technologies.
There are four basic battery technologies (five if you count nicad, but this is being phased out as a marine power source because of its toxicity to sealife), these are Alkaline, Nickel Metal Hydride (NiMH), Sealed Lead Acid (SLA) and Lithium Ion (LIon).
Alkaline cells are what the man in the street would call â€œbatteriesâ€. Theyâ€™re not rechargeable, but they’re cheap and easy to get hold of. Theyâ€™re used in cheap dive lights and backup lights. This is because a) theyâ€™re much cheaper than a rechargeable battery, charger and associated gubbins, and b) they don’t self-discharge anywhere near as quickly as rechargeables, meaning that you can leave them in your dive light between dive trips and expect them to be pretty much unchanged when you next come to use them (this isnâ€™t true of rechargeables). There are several torches that come in both alkaline and rechargeable version, the alkaline version generally being significantly cheaper (£40+ isnâ€™t uncommon).
Sealed Lead Acid
Sealed Lead Acid batteries are the traditional option, but while they’ve been completely outmoded in many applications, diving isn’t yet one of them. The biggest problem with SLAs is their low capacity to size and weight ratios, ie. to power a given bulb for a given time, the SLA you’ll need with be a lot bigger and heavier than the NiMH or LIon for the same job. This isn’t a huge problem in diving because what you gain in weight in your torch, you lose in weight on your weight belt. However: if you want big runtimes and a powerful bulb, your canister will look more like a dustbin; if you’re using steel twins, you may end up over-weighted; and depending on where you mount you canister, you could end up with a constant list in the water due to it pulling one side of you down. On the positive side, SLAs are cheap, don’t need to be carefully soldered/welded together and self-discharge very slowly. Disadvantages other than their size and weight are that they’re generally slow to charge and need to be kept charged to prevent damage.
Nickel Metal Hydride Cells
Nickel Metal Hydride cells have taken over from Nickel Cadmium (NiCad) cells as the â€œstandardâ€ consumer rechargeable cell due to their superior capacity. They’re currently the dominant force in rechargeable dive lights. They offer high capacities with relatively light weight and small sizes. Downsides to NiMH are 1) They self-discharge quite quickly 2) They have to be charged in a fairly specific way, so a dedicated charger is required 3) In order to keep the batteries in the best condition possible, they need to be fully discharged and recharged at least every 3 months.
Lithium Ion Cells
Lithium Ion cells are the current state-of-the-art, offering higher capacities relative to size than any of the other battery technologies mentioned. Predictably enough, they’re generally more expensive than the other three battery technologies. They’re also very fussy about their charging and discharging: discharging too much or too fast and charging too much will all damage the battery. Luckily there should be electronics built into assembled battery packs that prevent such conditions. Lithium Ion batteries are only currently seen in top end canister lights, but this will change with time as the price of the cells falls.