Diver UK – July 2019

LIGHTS

TO SUIT YOUR

POCKET

divErNEt.com

T

HERE ARE FOUR MAIN REASONSfor

using dive lights – to see in the dark, to

search in the shadows, to restore colour

and for signalling. And, much as we might often

need a big, powerful, long-burning, fully featured

torch, for much daytime leisure diving it can just

get in the way.

For a more convenient alternative, or for use as

a back-up, we need a light that’s inexpensive,

portable, easy to stow in a pocket or on a clip

and able to fulfill those four functions to an

acceptable degree.

It needs to compromise between a broad

beam that lights the way and a narrow one that

will illuminate crevices. A practical burntime

and a convenient means of powering up or

recharging is required. And any time your safety

could be jeopardised by light failure, at least one

back-up should be carried.

Performanceis determined chiefly by the

bulb, reflector and power-pack. These three items

control output or brightness, narrowness or

width of beam, and burntime.

Intensityor brightness is governed by the

inverse square law. It takes four times as much

output to retain the same brightness when the

distance to the object on which you shine your

light doubles. This also applies if you increase the

angle or width of beam to light a greater area.

Manufacturers usually describe output in

lumens. The figures given in the test are valid for

air, though under water output is affected by

colour absorption. Our eyes adjust to the

brightness of our light, so most that have a few

hundred lumens’ output will seem fine on a

night-dive. However, if another diver has a

brighter light, torch envy can set in.

LEDshave largely replaced gas-filled bulbs.

They are virtually indestructible, require little

power, can produce light with extremely good

colour characteristics and are inexpensive.

Colour temperature, measured in Kelvin, isn’t

that important for divers. Low temperatures,

such as 4500K, tend towards warm hues such as

reds that are quickly absorbed by water., slightly

reducing intensity and range. High temperatures

such as 6500K are biased towards blue colours.

In the middle range is 5500K, a “neutral” white

light. 5000-6000K is the default temperature for

many lights used for underwater stills and video.

Adjustable-powerlights can allow you to

minimise backscatter to see better. A low output

can make it easier to see things up close or

extend duration.

F

OR DIVING,beam anglesare described as

spotor flood. A narrow spot beam works

well in daylight or for looking into holes.

Only a couple of the lights tested had pinpoint

spot beams without edge lighting. Most had a

bright centre spot with dimmer, if still very

usable, light radiating out. This is useful for

seeing your surroundings, and makes for a good

back-up at night or in overhead environments.

A flood beam lights a far larger area, essential

for seeing where you’re going, such as in a cave

but less effective for looking into nooks. Those

used for diving are usually narrower than those

used for video

lights, which need to

be matched to the angle of

your lens or they will hotspot. Wide-beam

compact video lights aren’t usually much good

for diving.

Most dive-lights with a flood beam strike a

compromise that lets you see a fairly large area

with good distance penetration. Some have

adjustable focus, so the beam can be zoomed in

or out to narrow or widen it.

Smooth reflectorsare usually used for spot

beams, dimpled ones for flood beams. In either

case a well-designed reflector yields a smooth,

even light.

Light duration or burntimeis a consideration

if you want to use your light for several dives

without having to charge or change batteries.

How long are those dives likely to last?

Increasingly lights, even in the economy

range, use rechargeablebatteries, usually

lithium-ioncells. Their performance figures as

quoted by the manufacturer should be fairly

accurate – less so those of single-use batteries.

Some lights sold as rechargeables can also

accept single-use batteries if you can’t recharge

in time for your next dive. All but one of the

tested rechargeable lights have removable cells,

so you can just switch to a spare.

The GoBe is a sealed unit. This significantly

reduces risk of flooding through user error, but

you need to have time to recharge it. All of the

featured rechargeables use a USB charger.

All three common styles of switchare found

among our test group. The simplest is a screw-

down front bezel. Turn it the wrong way and

you’ll eventually flood your light. At depth,

pressure can also turn the light on inadvertently.

As long as you guard against this, the design

does eliminate potential leak points. You’ll

usually need both hands for switching.

A mechanical or magnetic switch turns the

light on and off but also enables adjustments

such as brightness or SOS functions. It can

normally be used one-handed. None of the lights

tested, except the GoBe, had a switch-lockto

prevent accidental switching on.

STEVE WARRENchecks out 10 dive-lights priced at

less than £100 to see if they have what it takes

Left: A 700-lumen, 30° beam pocket torch used as a primary

night-diving light.

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