What have you had on them up until this point, light-wise?
I typically have two larger plants in flowering at any time, and use a 400w HPS. I've found it to be absolutely perfect for my use, though if you can keep the area cool then there is no amount of light that these babies wont love.
As for Mr. Kelso's statement above... He is correct. You can typically find all the info you need by searching the Grow FAQ or the forum in general.