The primary light has one major purpose: communication. Beyond that, it also provides illumination in dark environments, from night diving to overheads, such as cave and wreck. Finally, it assists in bringing the colors to light, depending on the technology.
A primary light is one of the most indispensable pieces of gear because it allows the team to stay together with much greater ease and safety. Instead of being constrained to visual contact of the divers, the primary light allows a diver to broadcast their presence over greater distances. Now, instead of having to look for the diver, a teammate can simply look for the light beam or spot. And that makes all the difference in the world when it comes to smoother buddy diving.
As the primary role of the light is communication, it needs a few basic requirements.
1) Bright focused spot light
2) Dive time appropriate for planned dive
3) Enough power to illuminate area and cut through murky water.
4) Usable in either hand, with some facility to allow use of hands with light
Some nice to haves:
1) Light weight design for hand-holding
2) Easy attachment points
With that said, you have a huge catalog of choices to ponder.
HID vs. Halogen
In the early days of lighting, halogen reigned supreme. It's durable, low cost, and can powerful enough for most environments. It does not, however, have an accurate white color temperature, taking on much more orange cast to its light. It also is not a very efficient power source, requiring large amounts of battery capacity.
HID is much more efficient, allowing a much longer burn time as compared to halogen. It also is much brighter, roughly 5x the brightness for an equivalent watt halogen bulb. Finally, it's much whiter, making for better video lighting and easier to see. However it also has it's drawbacks, namely cost. Along with being 5X as bright, the bulb is also 5X as much. And as it is a much more complex technology, it is more complicated, requiring ballasts to regulate voltages to go along with those gas-filled bulbs. It requires a greater degree of care and maintenance when compared to the beater halogen lights.
Clearly, HID is the winner in current lighting trends, but it would be nice to get back some of the qualities of the halogen. . .
Lead Acid vs. NiMH
Traditional, power was provided by lead acid batteries, the same that power cars, motorcycles, and more throughout the world. As with halogen, the main benefits are cost and reliability. The sealed lead-acid battery pack is maintenance-free, in the sense that all you have to do is charge it. Memory effect is minimal, if you maintain the charging cycle on the battery, and the battery charges equally as per the voltage. The main drawback is weight: the lead in the lead-acid is obviously dense metal. Along with the weight, the packs are bulky, requiring larger canisters for the larger batteries.
NIckel Metal Hydride batteries are new on the scene, and possess some great qualities, namely lighter weight and greater capacity. My Pro-14 amp battery pack weighed in at ~12"+ long, and about 18 lbs out of the water. Meanwhile, the Helios 13.5 amp battery pack is roughly half the size. The main drawback is fragility, as the individual cells of the battery packs are not as sturdy as their lead-acid counterparts. Furthermore, the more complicated design of some packs has lead to some charging issues. But with that in mind, Nickel Metal Hydride offers a usable alternative.
WIth all that said, the choice of a primary light is up to you. Many primary lights possess the basic characteristics that make the light most practical.
The light beam should be focusable to allow for the beam size to be adjusted to provide the best spot in all conditions. Barring that, a fixed focus of reasonable size may also be used, provided the spot is bright enough for easy signaling.
The light is best when compact with a Goodman handle of some variety. The smaller the head, the more easily it disappears on your hand. Lights with larger ballasts, namely 18 watt and higher, often interfere with dry glove rings, but most don't mind with the increased light. The goodman handle provides an easy way for the light head to remain on your hand, yet still allow you to perform tasks, such as putting in your backup, adjusting your buoyancy, etc. The Goodman handle is best when adjustable, as you ought to be able to open you hand, and not have the light head slip off. Finally, it ought to provide a simple means to attach bolt snaps or loops, to allow for easy stowage when broken/not in use.
The light cord allows the battery to be carried on the waist, reducing the weight of the light head, and reducing the dynamic instability that would be caused by swinging that battery around on your hand. It also means that you won't lose your light head when it inevitably falls off your hand. It should be long enough to travel from the canister to the left hand with a minimum of tension.
The canister ought to mount out of the way, and in easy reach. It must also be removable to allow for ditchable weight. Traditional location is on the right side of the waist belt, where the lack of fixed buckle allows easy ditching, and where it can conveniently hold your long hose in place as well. A second buckle can be used to keep the canister in place, which facilitates getting out of the harness in the water (such as is required for smaller boats, etc.)
With these initial characteristics sorted, which one should you get???
Get the brightest light you can afford, but be realistic about your needs, especially when it comes to burn time. If you're just starting out, a dive longer than 2 hours is not a reasonable need. If you go with lead acid technology, it is reasonably affordable to purchase a 2nd battery that can be switched between dives. The smaller lead acid canisters are a nice alternative to the pricier NIMH
If you have the scratch, a NiMH battery is very very sexy, with the small size and ease of transportation. I would recommend the 9 amp version, as the increased length makes for simpler storing of the long hose. Just mind the charging issue (which can be remedied by unplugging/ replugging the battery every time you see the charger on the green light is a cheap (albeit annoying) fix. The 4.5 amp version provides 4 hours of burn with a 10 watt head, and is free of the charging issue.
For non-use, i.e. getting on and off the boat, the light should be stored in the up position, meaning the bulb facing toward the head of the diver. This provides the most protection for the light head, and also keeps the diver relatively streamlined, preventing a dangling light head from entangling in line, etc. IT SHOULD NEVER BE CLIPPED IN THE UP POSITION WHILE THE LIGHT IS ON! That ought to do it. ..
When on, the light should be clipped in a downward direction. This is accomplished via an attachment point at the back of the light. It allows you to illuminate what you may be doing below you, but more importantly, it prevents you from blinding (or "welding) or your buddies as you would if you clipped off with the light facing forward. This can be done for SMB deployment, stage switches, note taking, or any reason. It also allows you to have your light on during ascent, leaving it available for signaling your buddies should you need to, yet prevents you from welding them during deco. It also may draw up curious creatures from the deep, either mola mola's (good) or great whites (bad).
There are many different methods to attaching your light. Perhaps the first thing to remember is who will be affected by the way your light is clipped off: you. I hope that my buddy isn't so inept as to allow my light head rigging technique to affect his ability in the water. With that key point in mind, there are many variations.
1) Dual bolt snaps
I used this for many moons, but then realized that I would never use both attachment points at the same time. I kept getting line caught on it, and it made my light head look like a fishing jig. So while it was very easy to access either attachment point, it was a bit of overkill, and not very streamlined.
2) One bungee loop, and one bolt snap
The logic behind this was that removing the bolt snap from the front end allowed for more streamlined use, as you didn't get that "jingle bells" effect when signaling. It, however, allowed for simple clipping with the fixed bolt snap on the rear. Meanwhile, a small bungee loop attached by cave line allowed me to use a double ender to secure the front of the light. When in use, I could remove the double ender for nice free front end. I liked this method, but not as much as the next.
3) Two bungee loops, one double ender.
Two loops are attached to the light head: one in front, and one in rear. This allows you to use one double ender for attachment at either end. Use the front loop for stowage, use the rear loop for clipping while the light is on. Usually, I get in, unclip and activate the light, and then attach the double ender to the rear loop. It's now ready for clipping for 95% of the tasks I'd need to clip for during the dive, as my light will be on for the majority of the dive. When it comes time to turn the light off, I'm most likely in a non-stressful situation where I can use both hands to move the double-ender to the front loop. The only drawback to this system is the fact that the light hangs lower than it would with a bolt snap, but it's minimal interference when compared to the versatility and ease of use.
Regardless of which method you choose, realize that you need some forethought into how you use it. More important is to remember that you need to prevent blinding your buddies, so use the appropriate attachment points.
Entire volumes could (and should) be written on the proper and non-annoying use of primary lights. But that's another topic for another EE. For now, keep the light out of your buddies' eyes, but keep it where they can see it. Try and keep it as steady as possible to avoid throwing odd light signals. And make your light signals slow and obvious, with exception of "emergency" which ought to be fast and obvious. The more distinction you can make between the two, the better you'll be understood.
Check the sealing surfaces pre-dive. Always check the battery post-dive as any leak will be worse if you just leave it in your bucket. As always, rinse with fresh water post diving. Be sure to get the lead-acid batteries on a charge as soon as reasonably possible to prevent any long term memory issues. When not in use for an extended period of time, just leave on the charger. Perform a burn test every 6 months or so to monitor condition of the battery, and also to prevent any nasty surprises when you're three jumps into a cave, and have to come crawling out at night on a backup light with the ranger peeking over the edge, wondering why you're keeping him from steak dinner.
If any issues appear, first check to make sure the battery is charged. Be careful opening up the light; while not rocket science, it makes it harder to get the manufacturer to fix a flaw if you've gone mucking around inside.
Credits for this article go to the X-Forum at:http://www.5thd-x.com/xducation/xeducindex.html