The sky was without a cloud and the sun’s rays pierced through the water as we began our descent into Scripps Canyon near La Jolla, California. The clear blue water shifted to green during our passage through the thermocline. The brilliant red-orange drysuit my dive buddy wore turned to gray. At 90 feet, a rockfish eased itself through a crack in the overhanging canyon wall. White nudibranchs grazed on a forest of brown gorgonians. As we swam deeper and farther back under the overhang, I switched on my dive light and was surprised to see that the rockfish was endowed with a beautiful set of red scales. The nudibranchs were suspended in a tangle of red. The soft gray coating on the rocks turned out to be Corynactis anemones in all shades of pink. The color of my companion’s suit was restored as it was silhouetted against the emerald green sun.
Diving is, more than anything else, a visual experience. Memories such as I have just described are based on the incredible sights every diver experiences while exploring underwater. Often the visual impact is lost or not fully realized because one piece of dive gear was left behind – the dive light. Many divers feel the only time to take a light is on a night dive. They forget that water acts like a great blue-green filter, absorbing any traces of red light within a few yards of the surface. Underwater photographers use a strobe to fill in the lost colors. There is no reason underwater sightseers should not take along a dive light to achieve the same results. Many animals shy away from sunlight and hide in narrow cracks or under ledges. Only a handlight will disclose their reclusive lifestyles.
Most retail dive stores stock a confusing array of large and small, rechargeable and nonrechargeable, portable and surface powered lights. They are designed for such specialties as night diving, cave diving, spearfishing, photography or just poking around under ledges. Although important, price should not be the prime selective criterion. The larger the diver – the larger the light, is no longer an acceptable measure. There is some validity in choice of color for the purpose of maintaining a color coordinated diving outfit or high visibility underwater. The enlightened decision is supported by performance data and planned usage.
Beam quality: The most obvious thing to do when selecting a dive light is to turn it on and shine it on the wall. Check the quality of the beam. Is the illumination even or is it a jumble of bright spots and dark areas? Imagine trying to manipulate the bright spots of an uneven beam of light onto a small shrimp under a coral head or scanning for fish deep in a crack. Compare the color of the beams of several lights. Some will appear whiter than others. It makes sense to choose the whitest light for use in water that absorbs the red component of yellow rapidly.
Beam angle: The most useful area of coverage by a dive light depends on the situation. A very narrow beam (approximately 3-12 degrees) is needed for peering down long passageways or deep into a crack. It makes a good spotting light on a strobe or camera housing. A wider beam (15-30 degrees) is good for sightseeing at night. The broadest beam (40-90 degrees) is used for video and filmmaking. When beam angles are measured they include the central bright spot, which contains 90 percent of the light. The other 10 percent, which makes up the fringe, is useful for reading gauges at night while still preserving night vision and lighting up areas in your peripheral vision. The beam angle measured in air may not be the same as that seen underwater. If the front part of the light is flat the beam will get narrower; if it protrudes, the beam will be wider underwater.
Brightness: A dive light can be so small it is ineffective or so bright it ruins your night vision for anything but the center of the beam. A small handlight with a narrow beam will work fine for night diving if you are content to limit your peripheral vision. If you want to see all of the action on the reef then a light with similar brightness, but broader beam, is necessary.
Brightness is measured by several scales and can be confusing. Wattage indicates the actual power consumed by the lamp and can be calculated by multiplying the voltage of the lamp by the current (in amps) which flows through it. It does not take into account how efficiently the lamp puts out light or how good the reflector is at directing the beam forward. Terms like foot-candle, candlepower and center beam candlepower relate to the actual brightness of the beam of light at some point, but do not describe how much of the beam is actually that bright. The same amount of light could be directed into a very narrow, bright beam or spread out over a broader, less bright beam. Therefore, beam angle should always be considered when comparing brightness by the numbers.
Batteries: Batteries come as throw away cells or as rechargeables. Each has its advantages. Throw away cells should be used when you do not want to worry about whether your light is charged or not or where there is no electricity for charging. Unlike rechargeables, throw aways hold a charge for a long period (a year or more), making them good for emergency use. As throwaways run down, the light just gets dimmer and dimmer rather than falling off rapidly at the end of charge as with rechargeables. Throw aways come in various capacities. Alkalines hold the most power, by as much as a factor of five and are the most expensive. Heavy duty grade batteries have less power, but more than the least expensive grades. For high performance dive lights which draw considerable power, alkalines must be used.
Rechargeable batteries are ideal for divers who use their lights often or for high wattage lights. They are easily paid for after a few charging cycles. There are two types of rechargeable batteries, the ni-cad and the lead-acid. Ni-cads are more expensive than lead-acid cells, but are rated for more cycles (500 versus 100 approximately). Both types will lose capacity and cycle life if allowed to burn completely out. The light should be turned off and recharged when it grows dim. Lead-acid cells should be recharged immediately after use and every four to six months. Ni-cads do not require constant recharging. The burn time of a light is directly affected by the capacity of the batteries measured in amp-hours. This can vary as much as three times for the same size batteries. The most expensive cells have the highest capacity and produce the longest burn times. Generally, 80 minutes is the minimum acceptable burn time.
Lamps: All lamps are very similar in construction. They are made from a fine tungsten filament, strung between two metal posts, encased in a glass envelope. When electricity flows through the filament the tungsten glows and gives off light. Eventually the tungsten evaporates and the filament breaks, causing a “burned out bulb.’ Unless the glass envelope is filled with high pressure gas the tungsten collects on the glass walls and the lamp grows dim with age. Adding halogen gas takes the tungsten off the walls and redeposits it on the filament for a longer lamp life. Gases such as argon and krypton help the filament produce light more efficiently and with a whiter appearance. As a result it is well worth selecting dive lights that incorporate high pressure, krypton, or halogen gases in order to get as much as a two-fold increase in performance.
Handling: A dive light should be convenient and comfortable to use. If you travel much, choose the light that takes the least luggage space. To test comfort, hold the light in your hand to make sure the grip is not too large. On the larger lights most people find the pistol style grip more comfortable while they are in the prone position. If the light is to be used often out of water the hanging type grip is more comfortable. Smaller lights can be attached to your arm or camera using various holders available as accessories. Negative buoyancy is generally preferred. Finally, be sure there is a loop to attach a wrist lanyard so that you do not lose the light.
Accessories: The more accessories the better. They include 220 volt AC and 12 volt DC chargers, fast charge batteries and extra high power lamps. Mounting systems that attach to strobe arms and heads and cameras are useful. Protective rubber covers absorb sharp blows and guard against scratches.
Conclusion: Diving is a visual experience. In order to get the most out of it a light should be taken on every dive. Aside from being waterproof, a few key features should be considered when choosing the proper dive light. These include the beam quality, brightness, beam angle, type of battery, lamp design, size, grip and accessories. Try to imagine yourself using the light in the water, not on shore.