1st if your using cfl get as many as you can fit in whether its 4foots or the long bayonet singles which you can also get in a blue spectrum...if its 4 foots just measure the top inside and see what you can get in go for the brightest you can get for your money

2nd thing how many if you want to go max then see how many pots you can get in there then just minus 1 or even 2 prob be like 5 plants or so

also as there cfl they dont give off much heat so if your room gets a bit could like mine used to i jus put 1 golf ball type bulb in bit further a way and it warms the room up nicely