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As Sean alluded to, to minimize backscatter from particulate
matter and plankton in the water column the optimum angle to place lighting is
at a 45 degree angle to the subject from the viewer’s direction. An additional
method that is useful in special applications is to place the lighting behind
the viewer (but not in the sub). R/Jay Respectfully, Jay K. Jeffries Andros Is., Bahamas As scarce as the truth is, the supply has always been in excess of
the demand. -Josh Billings From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Sean T.
Stevenson 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 |