Choosing a Dive Light
Until recently, light strength was almost always rated in watts. A watt is a measurement of the amount of electricity that a bulb uses. When comparing similar types of bulbs, this can be a good indication of the power of a light. For example, a household 72 watt incandescent bulb will produce less light than a household 150 incandescent bulb. When comparing bulbs of the same type, a general rule is that the more electricity a bulb uses, the more light it produces.
However, when comparing dissimilar types of bulbs, a bulb’s rating in watts is not the best way to determine light output. Using household light bulbs as an example, a GE 72 Watt incandescent bulb actually produces less light than a GE 27 Watt LED. With the advent of new dive light technologies such as HID and LED, a straight comparison of power usage may not give a clear indication of which bulb will produce the most light.
Lumens are rapidly becoming the most common method of rating dive lights. Lumens indicate the amount of visible light that a bulb produces, and as such are a much better measurement than watts when determining dive light strength. A lumen is comparable to the light a single birthday candle produces when viewed from a distance of about one foot.
In the example given above, the GE 72 Watt incandescent bulb produces 1490 lumens of light, while the GE 27 Watt LED produces 1600 lumens of light. The 27 Watt LED bulb produces more light while using much less power. Dive light ratings range from 100 lumens or less for small, handheld lights, to well over 1,000 lumens for primary lights.
When selecting a dive light, a diver should consider not only the amount of electricity the light uses (watts) and the amount of light it produces (lumens), but also the <em>luminous efficiency</em> of the light. Luminous efficiency is a measurement of how many lumens the light outputs per each watt, and will affect the light’s burn time.
In general, LED lights are the most efficient type of bulb, with a luminous efficiency averaging between 60 and 100 lumens per a watt. Modern HID lights can also have high luminous efficiency, while halogen and xenon bulbs are often less efficient. Light manufacturers usually list the watts and lumens ratings for dive lights, and calculating the luminous efficiency may be a great tool in determining which dive light to buy.
A light’s burn time indicates how long the light will last on a single set of batteries or one full charge. The burn time will depend upon the luminous efficiency of the light, the strength and type of battery, and the type of bulb used. Often, divers must compromise between a light’s strength, burn time, and physical size.Adjustable Strength Dive Lights
Adjustable Strength Dive Lights
Many modern dive lights can be adjusted to control the luminous output. This allows the diver to use the light on full power, low power, and often a variety of settings in between. As a lower luminous output draws less energy from the battery, an adjustable strength dive light may be useful to divers who change dive environments often and do not always need full power, or who would like to be able to lower the power of the dive light to conserve burn time during a dive.
How is the viz? Water clarity will often determine whether a wide or narrow beam will work best for a diver’s purposes. In clear water, many divers choose a wide beam. A wide beam provides a large cone of light that allows the diver to view a great deal of his surroundings. However, in water with reduced visibility from silt or other particulate, a wide beam will tend to bounce off the particulate. This may reduce the distance a diver can see and may reflect light back at the diver. Most divers who venture often into silty or murky waters prefer a tightly focused beam.
A second factor that should be considered when deciding between a wide and narrow light beam is how far ahead the diver would like to see. A general rule for lights with similar luminous outputs is that the tighter the light beam, the greater the distance the light will penetrate. When comparing lights consider which is preferable: seeing farther ahead or seeing more of your surroundings.
Purpose of the Light
Why are you purchasing a dive light? The intended purpose of the dive light will help a diver to determine whether a wide or narrow beam is preferable. If the light will be used to peer in reef holes, a tight beam will often give the best light for the smallest power usage and luminous output. If the diver plans to shoot video, and needs to illuminate the environment, a wider beam will typically be better.
Back-up lights often have very narrow beams, as their purpose is to allow a diver to navigate out of a dive site in the event of a primary light failure, not to relax and enjoy the surroundings. They are great for problem management, but not for sight-seeing. Not every style of light will work well in every dive environment.
Arc or Angle of the Beam
Many dive light manufacturers list the arc or angle of the light beam. This is a useful measurement of focused light beam will be. Tight beams, or spots, are generally have and arc of 10° to 15° and wide beams or flood lights, typically have an arc of 50° – 90°. The wider the arc, the more of the surroundings a diver will see.Adjustable Beam Lights
Adjustable Beam Lights
For divers who change dive environments frequently, who use dive lights for a variety of purposes, or who simply want flexibility in their dive lights, light manufacturers offer adjustable beam lights. The method of adjusting the light beam varies between styles of dive lights.
Some adjustable beam dive lights use a metal reflector cone mounted around the light head. The diver moves the cone forward or backward along the light head to focus or scatter the beam, giving the diver ability to make very fine adjustments. This type of adjustable light head is common in HID lights.
Adjustable beam LED lights, on the other hand, usually do not employee moveable reflectors. Instead, they often incorporate multiple LEDs in the light head, a few close together near the center, and others farther out along the periphery. The diver may choose to use just the LEDs in the center or all the LEDs (or a combination of the two) by operating a switch.