i'm using 260 watts pc on my 75 gallon...
before that i was using 2 x 40 watts odno.
that still isn't much light. i couldn't get blyxa japonica to grow in my tank with that setup.
amazon swords grew in my tank just fine with 2 x 40 watts odno.
you can have a low light tank but just be careful with the plants you choose.
here's a pic of that tank with 2 x 40 watts odno. i grew mostly moss and swords.
http://i110.photobucket.com/albums/n...m/CIMG1504.jpg