When I think "dive light", I don't think about the little dry cell powered handhelds used by recreational divers, but rather the technical / cave diver style canister light, comprising a light head held in the hand, and a remote battery canister for power. I have owned a handful of these over the years, starting with a halogen video bulb using SLA batteries(12V), and most recently, a 50W HID setup powered by NiMH cells. Regardless of the unit, the basic setup is the same, with the bulb / arc assembly housed within a (borosilicate glass?) "test tube", and the reflector being completely independent of the bulb assembly, permitting axial movement for variable focus. The glass itself is not that thick - presumably, thick enough for the pressure, but thin enough to permit heat transfer to the surrounding water, providing conductive / convective cooling to the assembly. The HID setup is great - bright even compared to ambient daylight.
If you shine a light out your viewport, I forsee a problem with reflection off the viewport back into the cabin, as well as simply being too bright, too close to your eyes to permit effective outside viewing. Also, backscatter problems are minimized when your light source is out to the side, or at any angle other than your viewing angle - using a light inside the cabin means you will get every reflection from suspended material in the water, not to mention the fact that you need another viewport for the light to keep it separated from your eyes. Also, as you noted you need a lot of light to see effectively through water, and any technology other than LED is going to produce a lot of heat that you need to cool. Consider how to get rid of it.
-Sean
On Jan 8, 2009, ShellyDalg@aol.com wrote:
I've used regular scuba dive lights and they don't put out much light. I can see where an LED set-up would give diffused light without much distance capability. I wonder how a high power focused light shone from behind a viewport would work. I have a hand held spot light that's 12 volt and has 1 million candle power. It gets a little hot close to the lens but at 6 inches is only just warm. It can be focused into a tight beam and will run for several hours on it's batteries. It takes a lot of Duracells to load it up though. I plan on using it as a back-up inside the sub so will report on it when I take the sub out. Frank D.