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OK, I'll ask: Why?trevinkorea:For me, I just do a quick visual inspection, make sure it is screwed down properly, turn it on and put it in the water. If it doesn't work or if it floods, I switch to a back up.
Just a little advice though, if your light does flood at depth, putting it into a bucket of fresh water before opening it is a really good idea. I learned this the hard way twice.
I'm kind of confused by the pressure part... Water isn't compressible so I don't see how a light that has flooded at depth will have more pressure at the surface.trevinkorea:If your light floods at depth, It will have more pressure inside at the surface and the reaction of the batteries with salt water will increase the pressure even more. So, when you do open the light at the surface, the solution inside will cause the light head to pop off and shower everything in the area with watever mixture has been created. By opening it in fresh water it will not get you saoked or risk contaminating other gear. Besides, it's easier to clean the inside if it is already in fresh water when the cap is removed.
Last time my light flooded I opened it in the air and my nice new drysuit and wing got covered in battery water. Not a great expereince.
Oh, that makes sense. ThanksBill51:The chances are the light wont be completely flooded with all air evacuated. The remaining pockets of air will be pressurized at the same pressure as the water that entered and it will expand back to its original volume when opened at the surface unless there is a full two way leak and it forced water out on your assent.