just get a strain with 100% sativa genetics.. id go for dutch passion's durban poison it's one of the few un-touched sativa's that you can find.. they grow tall and spindly, in some ways, like a christmas tree. cool lighting you found.. too bad you can't use 4 foot tubes in limited grow spaces tho.. guess you must have a decent amount of space to work with.. which brings me to wonder why do you want to grow only narrow plants? you could have a great library of genetics all for yourself