Most divers, and British divers more than most, dive with torches. In the tropics, where the water is gin clear and the reef is bathed in light, the main use for a dive light is for looking in holes and crevices, and to bring back the red end of the spectrum.
In the UK, it's generally pretty dark down there. Silt filters out a lot more than just red light, and since most diving is done around wrecks, there tend to be plenty of dark places. A torch is not just handy, it's something you don't want to dive without.
I originally went for the ever-popular UK D4R torch when I first bought kit. It was big, it had two power settings, and I got it at a good price. However, when it flooded and the battery pack was knackered by rust, I decided it was time to go for something with a bit more Oomph. I wanted a cannister light - a torch where you have a small, light, handheld torch, powered by a large, heavy battery, placed somewhere convienient.
The main advantage to an umbilical torch is that you can stop worring about the size of the battery, as you don't have to support its weight in your hand. You can therefore have a brighter light that lasts longer than a simple handheld torch.
The main disadvantage to this type of torch is the price - a decent umbilical torch is going to set you back several hundred pounds. More than I had to spend.
But when I heard, on the hiddivelights Yahoo group, about an Airspeed book that told you how to build your own torch, I gained new hope, and ordered the book.
It's a thoroughly excellent book, that tells you everything you may want to know about umbilical torches. Sadly, I didn't have the time or the tools to build the more deluxe torches it gives plans for, but the cheap & cheerful variety it also talks about seemed to be fairly simple.
A day spent trawling B&Q, Wickes and Maplins got me all the necessary parts, and a trip to my girlfriend's father's workshop got my torch mostly assembled. A few finishing touches with a soldering iron later, and in the space of a weekend, for the sum of £100, I'd knocked up a fairly decent cannister torch. It looks totally home-made, but I didn't care, so long as it worked.
And since I was off to Stoney Cove just two days later, I got my chance to test it. I threw it in at the deep end and took it to the bottom of the 35m pit (As deep as I'm qualified to go at the moment, and as deep as I ever want to go while not breathing Helium - I feel noticeably narked at 35m). Tons of light, I could see just fine. Inside the Stanegarth, the amount of light it put out just blew me away - I was using a 35 watt MR16 bulb, twice as bright as my old torch had been. Even on the next dive, using only a 20 watt bulb, I was still impressed.
Sadly, it had leaked - I had neglected to add an O-ring in one place. I corrected that oversight, and it hasn't leaked since. My only complaint is that I can't fit a Goodman handle on it. Beggars can't be choosers, I suppose. I intend to upgrade it over time to a test-tube style light with bigger batteries, maybe even a HID, when I have the cash. In the meantime, I'm happy to stick to a butchered Maglite attached to a length of drainpipe.
If you have any interest in how I built it, then Read this.
In addition to my main, hip-mounted light, I also carry two small backups. Originally, I used the first dive light I ever bought, a UK SL4. Then I replaced it with two Pelican supersabre lights - they fit more comfortably as they take three batteries in a row rather than four in a 2x2 config. These put out a small but powerful beam of light, and are attached to my shoulder D-rings via SS bolt snaps. The other end is tucked into a bit of bicycle inner tubing, to keep it from swinging about.
