The "need" part is directly related to how much light you intend to use.
This thread covers that much better than I could(and probably in far fewer words).
http://www.plantedtank.net/forums/showthread.php?t=107303
Might as well do this one also: http://www.plantedtank.net/forums/showthread.php?t=184368
This thread covers that much better than I could(and probably in far fewer words).
http://www.plantedtank.net/forums/showthread.php?t=107303
Might as well do this one also: http://www.plantedtank.net/forums/showthread.php?t=184368