Im looking to build a system similar to the one seen here:
http://kstp.com/article/stories/S3395784.shtml

The issue im running into (and cant seem to find the answer anywhere) is the optimal spacing for a t5 fixture to cover my beds. The beds ive drawn up are 18ftX2ft, how wide of a fixture (number of bulbs and dimension) is optimal for this bed? I can also resize it to better fit a fixture (make it wider).

I keep reading that fluorescents only cover the space directly below them, then other sources say otherwise. The individual in the above video seems to have a bed wider than his light fixture, and he spaces them apart a about a foot as well by the look of it.

How do i know the best way to build my beds / which fixtures to buy to make sure my plants (Primarily lettuce ) will grow well?