the grow room is 2.7m wide and around 4.2m long. so i put close to each other 2x2x2 leds ( 3 rows). and have some little space left for some other things. Basically those 660w is recommended for 4x4 feet space one, for 5x5 feet i would go something more powerful, 800w or 1000w. But these 660 for me performs very good