By: John Bentley
Cave diving pioneers are quick to bring up the limitations of their giant canister lights compared to the more powerful handheld backups we have now. Their animosity is rightfully earned. In recent years the lighting and battery industries have made huge leaps of technology and that tech has transitioned to the diving world. Plastic light bodies have been replaced with low cost, highly durable anodized aluminum. Bulbs of all kinds have transitioned to simple, small and bright LEDs.
While we have rapid advances in lighting technology there are still choices for the technical diver to make. HIDs are on the market for specialty applications and rightfully so. Individuals will state that HIDs cut through the silt and light their large room videos better and there is validity to those statements. Outside of certain specialty areas of diving the least expensive and most simplistic lighting comes in the form of LEDs so let’s take a moment to focus on those.
To get started we should first understand how an LED works compared to its counter parts. “Traditional” lights create light using a filament which is sealed inside a vacuum. As electricity is run through the thin filament material it heats up and emits light. High Intensity Discharge Light bulbs (HID) work in a similar way however instead of a thin filament heating, a gas inside the tube is the material that creates light as a byproduct of electricity running through it. LEDs on the other hand are diodes, which, in simple terms means circuitry that only allows current to flow one way. In order for light to be the byproduct of a diode it needs to be constructed of some special materials, mounted, have appropriate circuitry and power and be fixed with an appropriate reflector device.
Video vs. Primary vs. Backup
LEDs emit light in a classic lambertian fashion, in that they evenly distribute unfocused light. For cave diving applications we need to focus that light into a central hotspot. That hotspot allows us to have an area with which to signal our dive buddies and prevent washout of their lights. Since overhead divers cannot easily use the classic scuba hand signals this hotspot is a requirement for emergency and regular signaling. 10-15% is an appropriate hotspot focus ring for diving. Spill over, or a wider angle of less powerful light, will surround the hotspot, typically reaching 60-80%.
The hotspot is necessary for two of the three kinds of lights typically in caves: primaries and backups. Primary lights are the main light with the longest burn time and most powerful beam. The primary runs the whole dive and is that individual’s main source of light to navigate and enjoy the cave. Canister lights, or lights with large external battery packs, were the standard identifier of a primary light but now are on the out with the industry’s adoption of lithium batteries. 5 or more hours of burn time are packed into lights that fit atop a diver’s wrist. Primary lights start at 1,000 lumens for 400 and go up from there. A good primary will have adequate burn time for a day of diving, modern rechargeable battery technology and either have a small external canister or be self-housed.
Cave divers, following the 5 rules, also carry two backups in case the primary fails. Traditionally one of these two lights should have non-rechargeable batteries. With advances in form factor and affordability of lithium batteries this rule is outdated and most backup lights have rechargeable batteries. Modern backups are more often just as powerful as primary lights but don’t have the burn-time requirements of primaries since they’re only used to exit a cave after a light failure. Backups typically start at 600 lumens at 70 and go up from there. These lights should be handheld, not “pistol grip” and the deployment and activation of them should be practiced outside of the cave with eyes closed to simulate a light failure. It’s becoming more common to carry a “backup primary” in addition to two smaller, lower burn time, lights. This second light would be the same as the primary and used to insure a comfortable emergency exit with plenty of burn time to continue the day’s diving.
The exception to the hotspot requirement is for photography and videography. When there’s a camera on the dive, hotspots are avoided to have even exposure. Video/photo lights are typically more powerful but don’t have the battery life. They also emit light of a similar color (referred to as a color temperature) to the sun for more natural looking footage.
Types of LEDs
There are currently three different methods for LED production: dual in-line package (DIP) surface mounted devices (SMD) and circuit on board (COB). While a few variations of these exist these three categories are an appropriate depth for choosing dive lights.
DIPs have been in production for decades and house a single diode on a single circuit. While still more efficient and longer lasting than other lighting technologies DIPs have been left in the dust by SMDs and, more recently, COBs. You’ll still see some dive lights with DIP technology, but those are quickly being replaced.
SMD chips are smaller that DIPs and can have 3 diodes on each board, even giving the ability for multiple colors on each chip. SMDs are often seen in LED strip lighting, are the light source for most LED dive lights and produce 50-100 lumens/watt compared to the 35-80 lumens/watt from a DIP LED. SMD chips have one circuit for each diode, and there are 2 contacts for each circuit (anode and cathode).
COB LEDs, the most recent advancement in the LED game, have 1 circuit per chip, with as many as 9 diodes per chip. This gives an extremely high lumen/watt ratio for COB LEDs and has given rise to their popularity for replacing bulbs for lamps and overhead lighting in homes. The downside to COBs is the spacing between the diodes. With so much light being produced in a small area (6 times smaller of an area than SMDs) efficient heat sinks are key to encouraging longevity of the LED.
So, which is best for diving? COBs are the most efficient for producing lots of light, but they haven’t been adopted by any manufacturers for primary or backup purposes. Many light manufacturers have begun using COBs for video lighting applications due to their high lumen output and even distribution.
Lumen vs. Lux vs. Others
When choosing a dive light the question of units pops up quite frequently. Between mAh ratings on batteries to lumens it can be confusing. Lumens are quickly becoming the accepted light output unit over lux with name brands like CREE listed them as technical specs. To boil down the technical jargon many people state “lumens are calculated and lux are measured”. This is and isn’t true. Both methods are SI measurements for light visible to the eye with lux being lumen output per square meter. This means that lux is a derivative of lumens and may, or may not, be more useful to the user due to its specific nature in relation to area. Like any measurement, the method of acquisition for the unit matters less than the availability of comparison. Without the ability to compare lights the consumer is left lost in a sea of conversions.
In early cave diving, and even recently, to get an affordable light that was suitable for overhead diving there was only 1 manufacturer, yourself. Homemade dive light discussions pop up in any google search, pretty close to the top. While many are simple internet divers posting on forums about their most recent gel-potting experiment on a household light most of the DIY crowd are intelligent and crafty. They helped original exploration by fixing halogen car lights to 12V batteries relying on the conductance of freshwater to not arch the current. Home builders also helped fill in the holes over the past 10 years while US manufacturers were slow to adopt lithium battery tech and LEDs. With this in mind it is currently more economical, in both time and money, to purchase a system from a reputable manufacturer than build one at home. Not to mention the benefits of warranties, replacement parts, and reliability.
With the ability for international sales and online research a surge of popularity has come for smaller batch dive lights made overseas. Out of this need some companies have emerged with QA processes, marketing platforms, US distribution and plenty of other “real company” attributes. There are still plenty of overseas lights out there without the backing of a real company and you don’t want to find out you got duped with cheap materials 2000ft inside a cave.