I've never used/ seen them before the other day, when someone posted this exact same question. They look pretty interesting, however I think I'm all set with running water that close to a 400w light bulb.......
i thought of this once befor to, I was thinking a 1 gal res that stays at 50 degree tempm then were the glass sheild is you could melt glass around 2 glass sheilds with 1/4 inch apartand then leave an in line and an out line made of glass then just hook up ur rubber hoses to it and pump that cooled water through the glass heat sheild and like quad the efficiencey. Ima go pattent it rite now.
i think if water flowed between your plants and the bulb, it would filter out some of the usable light? maybe not though. even if they didn't cost $400 i don't feel comfortable having 400w 1/2" away from water, with only breakable glass between it. air cooled is tried and true. and way cheaper.
heres the link i posted to the other Q http://www.1-hydroponics.co.uk/grow-lights/water-cooled-600w.htm u can see there that basically it's a glass cooltube, with precisely turned endcaps with rubber 'o'rings that seal the coolant in the tube & prevent it getting into the E40 socket. I was thinking something more like the water jackets u would use on an overclocked cpu / gfx card. U can watercool anything hot - as long as u can fabricate a water jacket the rest is piss easy