See my post under your Cat question. Also there are some very good sources of lighting such as
T5 Aquarium Lighting, T5 Fluorescent Grow Lights, Plant Grow Light Systems, Horticultural T5 Grow Light, T 5 Grow Light I use the New Wave brand. Have used others, but this seems the best value for the money and best light output.
I have several 4 tube 48" fixtures, one two tube 24" fixture, one 8 tube 48" fixture and several CF t5 high output. So I have a bit of personal experience. The 4 tube 48" seems to be the "sweet spot" as far as I can determine. The 8 tube I have measures at least 3600 FCs at approx 8" (or so - I am going from memory here) which is too high for most orchids with a 12 hour "on period". I use it for growing lettuce, spinnach and raddish which all require extreme light. There is no (absolutely none) tendency to bolt with 11 hour "days" and 60 degree temps. This is pretty extreme for your orchids.
I use 4 foot 4-tube fixture for my orchidarium with great results. It measures approx 1800 FCs at 12" near the uppermost orchids. I run it for 12 hours in winter and 14-16 hours during summer. Here is picture:
I use a mix of compact florescents and a 2-tube fixture in a grow window to supplement south-facing glass.
In short - yes, t5 tubes can be used quite successfully to grow orchids. So can t8 fixtures from Home Depot.
Indoor lighting systems
Linear Mode
