I think he used HxWxL as his equation not LxW.
thats correct, a square foot is HxWxL. so a 10x10x10=100sq ft, if that helps you understand a little better. So simplicity, lets say my room is 10x10x10 (pretty close to my actually room anyways) so my thinking is that 1 600w HPS would cover a 5x5x5 and then the other would be 600w or 95k lum's for 5x5x5 for a total of 190k lums and the other option is 600w + 1000w HPS or 230k lums for 10x10x10.