small grow tips?

Hey! Hi guys i've finished my first grow with 2 plants succesfully a couple months ago and i want to do the same with 1 plant this time.. not something big just personal comsumption. I was reading some threads on the internet and I am very confused about the grow area ... My closet is around 6x2x8 and i want to know if it's a big issue if growing only 1 plant? I read that you must have at least 6000 lumens per square foot.. but if i grow one plant in a big space like that my light output to the plant actually will not be more efficient than in a 2x2x8 area ? I just want to know if it's true and I should do a division in my closet for just 1 plant or that doesn't matter and i should't care about that ? I made my first grow with 4 feet fluorescents all the way changing light color between stages and did great.