Reconfiguring shelves - lighting question

[boytjie]

Hello all you indoors-under-lights growers, I'm thinking of reconfiguring my setup and have a question for those with solid T5 experience. Currently I've got two four-bulb T5 fixtures, one per shelf on a two-shelf arrangement. I'm toying with redoing things to hang both fixtures next to each other, effectively giving me a single eight-bulb fixture. How much distance would I likely need between bulbs and plants (Catt and Dendrobium alliance on the top shelf?) Also, would there still be enough light about three feet below that shelf to grow Paphs and Bulbos, bearing in mind that they'll also have pots overhead, further shading them from the light source?

Hope this isn't all too confusing... Thanks!