With water cooling I can put the light much closer to the plant won't this more than make up for the 2 pieces of glass? I would think getting the powerful light so close to the plant would yield great results.
I would think with light passing throught 2 paynes of glass and water, it would lose a lot of its intensity therefore I think it would perform a lot worse.. (watercooled). I have used air cooled hoods and cool tubes with 600w HID bulbs and had my plants within 8" and no burns.
Wow I did not think it would reduce that much the heat. My friend has a 400W (not air cooled) and at about 12-16'' from canopy you can see some slight drying from the heat