If you can manage it, put 4 lights together side by side. You'll get plenty of light to grow paphiopedilums and phalaenopsis and maybe some other genera. Get a humidifier and a fan - those ballasts can throw a lot of heat!
thats how mine is set up. four bulbs above each shelf. but i dont know how i will be able to get enough light for the catts without buying a whole new set-up and spending loads of money