In a perfect world, all underwater operations for public safety dive teams would take place in crystal-clear water with perfectly brilliant ambient light. Perhaps in that perfect world, many of the tasks carried out by PSD teams would also be unnecessary. But in the meanwhile, down here in the real world, we are called on to work in conditions to which we must bring our own lights if we want to have any illumination at all.
There is no generally used everyday technology that has undergone as many radical, fundamental changes as portable lighting; nowhere is this more apparent than with underwater lighting. Moreover, the changes have been complete, affecting both the power source delivering the energy and the lighting mechanism that converts that energy into light. We have, in effect, witnessed a revolution which has changed the way we approach limited visibility diving.
On first glance, the most obvious and most dramatic change has been to the device that converts chemical energy directly to electrical energy: the battery. As consumers, we are familiar with two types of battery: disposable and rechargeable, and both have changed dramatically in the past 10 or 15 years, which in turn has allowed the folks who design and manufacture dive lights to get pretty creative with their products.
The oldest form of rechargeable battery is the lead-acid wet-cell battery. What seems like a lifetime ago, if we wanted to take a “really powerful” light with us into the water to illuminate some particularly tricky and delicate operation, we took a light powered by a lead-acid battery. The first generally available semi-commercial lights made for cave diving — and used by PSD teams for low-light operations — were very heavy, very bulky incandescent lights using this type of power source; for all intents and purposes, a 12-volt motorcycle battery.
At some point the big improvement to the liquid electrolyte battery was the sealed valve regulated lead–acid battery (VRLA battery): popular in the automotive world, and cribbed by makers of underwater lights. These were still heavy (lead, right) and bulky but were somewhat easy to handle and less volatile during recharging.
Other portable rechargeable batteries that have made a showing over the years as the power source behind underwater lights include several “dry cell” sealed units. These were increasingly more powerful (power density) and developed for appliances such as mobile phones and laptop computers. Nickel–cadmium (NiCd), nickel–zinc (NiZn), nickel metal hydride (NiMH), and lithium-ion (Li-ion) cells.
In the underwater lighting market today, lithium batteries, and particularly Li-ion, seem the dry cell rechargeable that is most used. Lithium-ion batteries are common in most consumer electronics because of their energy densities, no memory effect, and only a slow loss of charge when not in use. They work very well in underwater lighting systems.
More on lithium cells in a moment, but now is a good time to sort out a couple of terms commonly used when we talk about lighting for divers.
In the days of incandescent lighting, we referred to a light as so-many watts and we accepted that as a way to grade how bright a light was. A 25-watt light was dim and a 150-watt light was much brighter, almost a spotlight. One of the early underwater lights this author had was 50-watts and, compared to the lighting used by the rest of the dive team, seemed bright enough to illuminate the wreck of the Titanic.
In fact, a watt has nothing at all to do with measuring how much light a light bulb or light source produces. A watt is the amount of power needed to move a one kilogram (2.2 pound) object at a speed of one meter per second against a force of one Newton. If that sounds a bit too close to the Physics 101 class you dropped out of your first year of college, let’s use terms we can all understand. Watts are a measure of the amount of energy something either uses or produces, and for the record, 746 watts is equal to one horsepower (nothing at all to do with light… well, not directly).
Lumens are a better unit to use. They are a measure of the perceived power of light that we can actually see. The nuts and bolts of what a lumen is and how it was derived is a little more complicated than that, but essentially, when it comes to comparing how bright a light is, specifically an underwater light, we are better off using lumens. In fact, in many jurisdictions it is required by law that lamps used for lighting are labeled with their light output in lumens and not watts. For example, an energy-efficient bulb that claims to be the equivalent of the “old-school” 60-watt tungsten bulb that most of us grew up with must have, by law in the EU, a minimum light output of 700-750 lumens. Clear as mud?
Having arrived at a relatively easy and standard unit of measurement to gauge the effectiveness of lights, let’s look at the apparatus producing the light itself.
Many of the truly tough and dependable lights being used by technical divers, military divers and PS divers these days, use light-emitting diode (LED) light sources, either an array of them or a single LED. This technology has revolutionized light design, function, and dependability. A quick glance at the product catalogs of the major underwater lighting companies shows that LED lights are the current wunderkind of the consumer lighting world. More specifically, LED lights are being used more and more by PSD teams because of their robustness, efficiency and relatively high output to dollar cost.
And the market has several options available.
Among the many US-based companies, Light Monkey out of North Florida produce what they term LED Primary Lights in three different power levels. These lights are the traditional canister lights and the battery canisters are machined from solid Delrin plastic with the light head for their “top-of-the-line” model machined from aluminum. These lights are warranted to a depth of 500′ (150m).
The company’s brightest offering is powered by a 20aH Li-ion rechargeable battery providing 480 minutes of burn time and producing 1100 lumens @ 5600 kelvin.
Hollis, another US-based company that markets a range of dive gear that runs from rebreathers to mask-straps, sells a similar LED canister light system they call the LED25. It is powered by a lithium-ion Polymer rechargeable battery, and it burns at 1250 lumens for five hours.
However, canister LED lights are becoming old technology and as more advances are made with the power packs driving the LED “bulbs,” completely hand-held systems are becoming more popular. This option – either hand-held or attached to a helmet for more efficiency – is more compact and therefore preferred by many PSD teams.
The smaller hand-held LED lights (often referred to as back-up or secondary lights) produce as much or more light than the old generation canister lights with far less clutter.
Typical is the Light Monkey backup LED powered by a 2.6aH Li-ion rechargeable battery and producing 600 lumens at 5600 kelvin. This very small, very tough light provides 210 minutes of burn time on a single charge and weighs 400 grams, less than a pound.
But perhaps the most impressive “new generation” underwater lights are from Cathx Ocean. This European company develops advanced lighting systems for divers, ocean vehicles and fixed subsea and surface installations. The company uses proprietary and patented technology and really advanced microprocessor control and monitoring in all its lighting systems, including its PSD lights and video systems. In other words, they produce lights that are made for commercial environments and extraordinary service conditions, and their engineering philosophy is that NO failures are acceptable. Unlike their competition in the dive light market, Cathx are primarily a lighting technology company and the PSD and technical dive community have not been their primary focus, although this is changing. Their hand-held Ethos lights are currently under testing with the police divers in a large US city and, to date (12 months in), there have been zero light failures and a lot of positive feedback.
For the record, its Euphos hand-held light has user-controlled variable power output with 75 minute burn time at full power (1250 lumens) and three hours burn time at medium power in a tough anodized or Teflon finish on marine grade alloy.
Whichever way we look at it, underwater lighting across the board, hand-held, canister, LED and so on, is remarkable compared to that old lead-acid monster I started out with. The profiles now are tiny and compact, the light output remarkable, and – perhaps the most important improvement – their reliability is as close to perfect as we can hope for. Cost, too, is dropping relative to performance. Good lighting is not cheap but lumen for lumen, the price of underwater lights has dropped consistently. And in any event, when conditions call for light and plenty of it, cost is a distant second to value.
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