you could also use mirrors as reflectors. mirrors reflect 99% of the light, so placing mirrors around your plants would boost the lux... as Mal has already said, common florescent lights
won't provide enough oompf once the plants get big, so eventually you might want to ugrade
your lights. LED lights are getting better all the time, with the best energy-to-light efficiency
of any artificial light source.
plus LEDs are 'tuned' to the proper light color (mj plants want green and red light to grow).
LEDs are expensive, but should last years...
good luck