Just a quick nitpick, Josh, but can we keep the social groups for socializing and the general forums for orchid-growing info? Not everyone is a member of every social group and by holding culture discussions there we exclude many forum members. I believe when the social groups were started there was concern that they might draw valuable discussions away from the forums and diminish the value of OB as a whole. Thanks!
britbloke, a lot is going to depend on where your particular pool cage is located and how heavy the screening is. The only real way to determine light levels in your situation is to actually measure them at different times of the day and maybe year (though in FL you won't see as much variance as folks further north). A basic light meter costs about $30 and you can also use an SLR camera to get a good approximation of footcandles. I'll look around for some instructions on the latter and get back to you when I find a link.
--Nat