A slight modification to this mounting method is to use a simple plastic weight belt buckle, which is slid on to the waist strap and used to hold the light in place - this system is excellent for UK RIB diving, in that you can undo the waist strap ready to get out of the water at the end of a dive and the battery canister is still held in place.
The Extreme Exposure lights have an excellent battery connection system. The system has no free floating wires, which can fail and break with the constant connection/disconnection for diving/transport that would occur. The Extreme lights use positive mating banana plugs which, allow the lid to be mated to the battery connections for use.
The light head is a "Goodman handle" which is the wrap round hand / palm grip style. These handles give you back your hand for working on things whether that be a scooter trigger or a lump hammer. The length of the cord is kept to an absolute minimum which is effectively the length needed to go into the left hand whilst the left arm is fully outstretched in front of you..
Why is "Butt" mounting
Many people believe that butt mounting is more streamlined, however the light on the hip is in the lee of the shoulder where it is protected.
The cable on a butt mounted light will need to be extra long which potentially will catch on everything unless it has some routing which is a real mess and interferes with the stages and all of the other gear.
Butt mounted lights are very difficult to work on with one hand (which is all you might have free) in an emergency - e.g. trying to take it off to free yourself.
The position where the battery canister would sit is where we keep reels and/or the lift bag in wreck diving. We park our long hose under the canister in its routing. Note that the long hose does not need the canister to sit properly, but it is much neater, and the hose will be tight to that point and not catch anything
Hanging a bouquet of backup lights from a tank d-ring is dangerous and impractical. The location is a natural snagger of everything, they slap back and forth on the tanks breaking the filaments in the bulbs. They are in the way of other gear and access to them is blocked by other gear, and it is impossible to properly deploy them.
The best backuplight available today are the Extreme Exposure Scouts.
Bulbs & Batteries
High currents and alkaline batteries don't go well together (Lithium's don't like high currents either). NiCds and gel lead-acids are much better in this respect because of their low-internal impedance's: the terminal voltage remains about the same irrespective of the current drawn - so the Primary light (needing 50 watts) needs to be driven from a Lead acid battery. NiCads have the unfortunate characteristic of working perfectly then tailing off very quickly. As such you may not notice this and be without light before you can get a backup light deployed.
For the backup lights it's hard however to beat alkaline batteries capacity for their size. Also as alkaline batteries die slowly its possible to "see" the backup failing and prepare either an alternative light or change the dive team order to protect the diver without a light. Nicads work full tilt boogie then fail rapidly, as such they don't lend them selves to a backup light application
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