I found this thread: http://forums.gardenweb.com/forums/load/lights/msg100150263074.html?11 combined with this wiki page: http://en.wikipedia.org/wiki/Lux to be very helpful. Looking at the amount of lumens the bulbs put out, not watts, I found that two T8 bulbs produced a good amount of lux for a 4ftx1ft area. It was comparable to the amount of lux for "full daylight" according to the wiki page. But not all T8s produce the same amount of lumens, so you should do your own calculation. (Lux = lumens divided by area. So two 4ft T8s span about a 4ft by 1ft area). Of course, not all of the light is staying in that 4'x1' area, but I thought it was a good enough approximation, and one that will be more true if you use shiny stuff to reflect the light back onto that area. One note of caution - the thread I linked at one point confused "ft-candles" and "lux." A foot-candle is the imperial measurement of amount of light per area. Lux is the metric measurement. One foot-candle equals about 10 lux.

Good luck!
Liz