Diver Tests Extra - Lamps

EXTRA

March 2000

LAMP STANDARDS

COMPARISON TABLE | HOW DO THEY PERFORM? | TORCH DOs & DONTs
Put underwater lights costing less than Ł100 on the spot in a 30-torch beamfeast, and the result is a surprising degree of diversity. John Bantin enlightens us
As every diver soon discovers, any item with an airspace which is taken under water is liable to leak at some time. Diving lights are probably the prime offenders. For that reason, when we approached UK distributors of diving equipment in search of subjects for this test, we were unsurprised to discover that many had decided to stop selling them - they were far too much trouble.
Of course, there is still a great selection of lamps available, but when we added the proviso that they should be suitable for use as a primary light during a night dive and should retail for less than Ł100, the list began to look rather shorter.
In home waters you normally need a lamp as soon as you get more than a few metres from the surface. It's essential if you are to read your gauges properly in the gloom. A lamp is also useful for looking into any space where ambient light does not fall, so one could say that a good light is an essential item of diving equipment.
In clear water, divers are less inclined to use a lamp during daylight but a powerful one will reveal objects and animals in their natural colour.
Some of the cheaper examples of torches sent for our test were on the margins of being mere back-up lights. No diver should go in relying on a single lamp. Besides disastrous floods, batteries and bulbs can fail. You should always carry a back-up which will see you safely back to the surface and the pick-up boat if need be.
For that reason it might make sense to use two cheaper lights (from this selection) than to do in all your money on a doubly expensive item which, despite its high cost and spec, could still leave you in the dark.
Rechargeable lamps tend to cost more than those that use dry batteries. They usually give out a brighter light but for a shorter time, and you must have facilities to recharge them. This might be easier said than done on a liveaboard that runs its generators for only a few hours each day, when you need at least 12 for your lamp ni-cad.
Some of the dry-battery lamps included look almost indistinguishable from their rechargeable siblings. In fact you can often substitute ni-cads in the appropriate size to fit, but be aware that the bulb wattage might need changing to suit.
We tested all those units that used dry-cells with high-energy alkaline batteries. It makes no sense to use inferior batteries, because they might not see you through a dive.
You've probably noticed that the headlamps of expensive cars seem to be getting smaller. This is because bulb technology makes it easier to design a smaller reflector that is very efficient - often more so than larger reflectors. Many new diving lights are taking advantage of smaller bulbs and can be very effective with quite small reflectors, too.

THE TEST
We compared the lamps by checking the diameter of each beam (and hot-spot) with each light positioned under water at the same set distance of 1.5m in a swimming pool, and measuring the maximum brightness of the beam centre on the pool wall. (The results are what you see in the circles alongside each lamp test.) These measurements are suitable only for use as direct comparisons, lamp to lamp.
More importantly, we looked at the shape of each beam. Many lamps also gave a peripheral halo, in some cases around 2m wide at the throw distance of 1.5m. Though this was merely a glimmer on the light meter, the eye can adjust for it and it is often comforting to know what loiters in the periphery of your torch beam.
Some lamps give an intense but narrow beam, while others give a broader, more general light. Which you prefer is down to personal taste. The brightness shown on the table is a measure of how bright each lamp was in comparison to the least bright, which was assigned a factor of 1.
Remember, however, that brightness alone can be misleading, because our eyes have an amazing ability to adjust to many different light levels. You will probably notice how powerful or puny your own lamp is only when diving with someone whose own lamp gives out a markedly different light.
We photographed each beam to show you the shape. This was done at a distance of 1m in a tank. These photographs should not be used to judge the brightness because, just as your eyes adjust, the camera exposure was adjusted to give the centre part of each beam the correct exposure.
We also weighed each lamp in (fresh) water. Positively buoyant items can be difficult to locate in the dark, even if they are securely attached to you, and a lamp should be negatively buoyant, though not to the extent that if you put it down for any reason it dramatically affects your own buoyancy.
The amount of airspace affects the weight of each lamp in water, so some of the big, heavy lamps weighed less in water than some smaller examples.
We also measured the diameter of each reflector to give you an idea of comparative size when looking at them in the pictures.

COMPARISON TABLE | HOW DO THEY PERFORM? | TORCH DOs & DONTs

Appeared in DIVER - March 2000