Well, in that case, you'll probably get a lot of thoughts here... in photos we would use 50w per Sq ft, autos you can get by with less. I'm about to fire up a 4 cob 200w unit, It'll go in a 4x4 tent, but I'm only expecting to cover 1/3 of it. If your usin them in the veg area (2x6) you won't need all 6, more like 3... in the main area (looks like your talking photos) your gonna need more light. I've seen it said that a 50w cob puts out approx the equivalent of 150w hps. In a flowering 6x6 area, you'd be looking at around 1800w this would work out to 1800 ÷ 150= 12... so 12 cobs arranged over 6x6.