I have posted up info on this under the newbi section, i would also disagree with the dude above, if you blast the plants 24/7 with a fan it puts its energy into its branches, however you want it to put its energy into bud not branches, let the fan air hit a wall the plants get the air 2nd hand, a light breeze is enough and it only needs air when the lights are on, once again please look for the newbi sec, its there to help, nuff said.
p-s A gentle light breeze gives you the best of both worlds, strong branches that will support nice bud, i also pics up at (indoor grow) under bangers green room worth a look nice snaps that were put up on fri night, best of luck to you, try find the newbi sec with the HELP info.