sizing T5 fixtures

[Ross]

If it's any help, I grow lettuce, spinach and radish under my 8-tube fixture which sits about 12" above the plants. They covet full sun and as I recall I measured over 3500 foot-candles at 12" (something like that.) I feel strongly there are few orchids that would want that high a light for 10-12 hours so feel free to move lights higher still (or drop the shelves). I'd bet 18" will do just fine for most Phals, Paphs, Masdies and most Angraecoids. A good light meter will help.