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Every other page in a scuba magazine is an advert for this weeks best dive light. What with Halogen, HID, and LED,  and not forgetting, Krypton, Xenon even HMI bulb types, its a mine field, and lets not even get into battery technology! Here's a few observations with regard to about a dozen of the various models available. Most torches are rated by the power that the bulb consumes i.e. 5 watt or 50 watt, unfortunately power consumption does not necessarily mean brighter light.  Dive lights come with handles, either lantern style for carrying or Goodman style to wear on the back of the hand. For lights with larger battery packs, umbilical cables that link battery to light head are popular.

Halogen Bulbs are probably the most popular bulb option, because of their cheap replacement cost and robustness. Primary Halogen dive lights often boast power outputs up to 50watts, but generally 35watts is sufficient.  Halogen light is ideal for general lighting, but can appear slightly yellow when used for video or photography work. A plus for halogen is that the bulbs are often replaceable with those obtained in car accessory shops, as they both generally share 12 volt technolog. Halogen light can be focussed easily and the bulb technology allows it to be dimmed. Less light output can be useful to conserve battery power. Halogen bulbs tend to dim when battery power starts to fail, the dimmed bulb can stay illuminated for some time before going out completely - handy if you are still in a cave or wreck!

H.I.D bulbs are very fashionable at the moment, High Intensity Discharge (H.I.D) systems use electronic wizardry  (voltage invertors) to increase bulb temperature and therefore brightness. HID bulbs are very efficient with battery power and can produce massive equivalent power outputs, with low current drain. An equivalent 50 watts of halogen power can be reproduced from only 10 watts of HID bulb. HID battery packs can be smaller, often last far longer than the equivalent Halogen. HID bulbs give of a dazzling white light, that can appear blue underwater to the naked eye. This blue light is excellent for underwater video enthusiasts. The HID bulb delivers a beam of light that has a spread often less than 10' arc. This appears like a "light sabre" underwater. HID bulbs are quite useful in poor visibility, due to the bulbs tight beam. HID bulb brightness can place very bright "hotspots" into video or photography images, that effectively over illuminates the target. Some manufacturers provide a movable reflector that can reduce the "hotspots" common with HID, while others use frosted glass as a diffuser...HID technology sounds perfect doesn't it? The down side of all this  brightness, compactness is fragility and expense. Some HID bulbs are like glass slippers and replacement bulbs can be very costly.

LED bulbs have come a long way since early digital watches. LED's come in sizes and outputs that now make them extremely useful as primary illuminators rather than just status advisers. LED bulbs have a very low current drain but produce a very white dazzling output. The latest LED bulbs can even be tightly focussed. The Monostar head from Greenforce gives a light beam akin to HID with even better battery life - it can even be dimmed to conserve power. The beam spread and bulb whiteness is very useful for image capturers, both video and photo. LED bulbs are predominately between 3 and 5 watt power outputs, soon to be topped with 20 watt power. LED bulbs have been available in back up torches for a while, the bulbs are ultra reliable and offer enormous durations.  The newer primary LED dive lights can have multiple bulbs that give bulb redundancy and very useful brightness, with up to 30 watts of power. In 2006 Greenforce lighting introduced a new type of LED bulb that is both incredibly bright and tightly focussed - these hybrid LEDs' will certainly give HID bulbs a run for their money.

When purchasing a primary dive light you should decide on traditional pistol grip or lantern /goodman  handles or, the umbilical system with the light head remote from the battery pack.

Remote heads are usually very powerful, and much less cumbersome than an equivalent powered lantern grip light. Traditional grip lights are cheaper than most umbilical models but do get dropped more often than remote head units. Ouch!

BACK UP LIGHTS

The smaller dive lights that fill divers Christmas stockings around the world  have turned from boy scouts toys to pieces of high tech gadgetry. Back up lights nowadays can have multiple LED bulbs or xenon or   krypton bulbs. Back up lights by virtue of their smaller sizes can have crush depths over 600m. When buying any dive light its advisable to get a model with incredible depth ratings. The deeper the depth rating, the more times the light will survive multiple shallower  depth excursions. Dive lights should ideally be constructed with a cylindrical shape. Lights that have a round body as opposed to square, will remain water tight for longer.

Above, a selection of popular back-up dive lights. The green light in the left photo has a depth rating of 152m (500 ft) The batteries in the centre shot were inside the green light at 313m (1032ft). The green light was one of a pair, where only one survived the dive. As you can see the batteries didn't fair too well either - check out the flat sides!

Hope you found all this illuminating... start the car  ;-)