2ft vs. 4ft T5 fixtures
 

I have a relatively small collection. 4 paphs, 1 phrag, 2 noid phals, a noid onc and den. I really only care about my paphs and phrags since the noids were more or less gifts that I'm just maintaining and I never throw away plants. Anyways I've been reading that light is less optimal at the edges of a fixture so i'm wondering if my setup is good enough? I keep the slippers in the center and all the ones I don't care about at the edges. These are HO T5s that supposedly put out 8000 lumens. My plants are about six to ten inches away from the fixture. I'm thinking that for such a small number of orchids this should be enough.

Thoughts? Input is greatly appreciated..

For this amount of plants, 2ft should be enough, and as you said, keep the Paph in the center and the Phal on the sides. If the phal don't have enough light, you will see them growing sideways towards the light... if you have a windowsill, they'd be even better there, with no need for artificial light !

I believe you're thinking about the plants and the lighting in sort of a backwards way. right now you seem to be giving the ones you prefer the better conditions, rather than matching the light levels to the needs of the plant. For example the dendros and oncids require more light than the paphs and phals, so they should be at the middle under the light, where it is brightest, and the lower light plants can surround them as they prefer lower light levels so can be farther away.

Your subject queried 2 foot versus 4 foot bulbs, but your commentary never mentioned it, so let me give another take on that.

2 foot bulbs consume 24 W of power each, while a single 4 foot bulb is a 54 watter. Therefore you get about 15% more light from a single big bulb than two small ones.

additionally, if you view the "usable area" under a fixture to extend approximately 1 foot around the perimeter of the reflector, then a 2-bulb fixture, being roughly 9" x 24", gives you a usable area of 2.75 x 4 feet, or about 11 square feet. A single, four-foot bulb fixture is about 6" x 48", so gives a usable area of 2.5 x 6 feet, or 15 ft.².