Recreational dive lights and cave diving lights have the following in common: they both emit light; they both work under water. At this point similarities end.
The typical recreational dive light consists of a self-contained light head, comprising both the power supply and bulb. Attached to the light head will be a handle — usually a pistol grip style unit. Finally, to attach the light to the user’s wrist, there will be a lanyard. All of these elements combine to make the typical recreational dive light totally unsuitable for cave diving.
Cave diving lights have evolved to overcome these limitations and meet the specific needs of cave divers.
Modern cave diving lights are powered by a 12-volt Nickel Metal Hydride (NiMH) or lead-acid (gel cell) rated at 4 amps or greater. Their light heads employ a 10-watt or larger High-Intensity Discharge (HID) bulb, encased in a waterproof, test-tube-style lens and surrounded by a compact, focusable reflector.
Innovations such as NiMH batteries and HID bulbs enable today’s cave diving lights to be substantially smaller and lighter than their predecessors of just a few years ago. At one time, the typical cave diving light consisted of a battery canister the size of a large Thermos, powering a 50-watt quartz-halogen bulb. It would have a theoretical"burn" time of three hours or less. In contrast, a modern 10-watt HID bulb outputs roughly the same amount of light — at a much higher color temperature — and can last up to four hours or more when powered by a NiMH battery canister the size of a Coke can.
Another area in which recreational and cave divers differ when it comes to lighting is the use of backup lights. Despite recent innovations, dive lights remain among the least reliable pieces of equipment divers carry. For this reason, cave divers carry two additional battery-powered backup lights in addition to their primary. These compact units are typically powered by four AA or three size C alkaline cells.
Recreational divers are taught to carry at least one such backup light. Unfortunately, most do not. This is one of the contributing factors to the more than 300 incidents in which divers without proper cave training have perished in underwater caves.