why do we use square feet to measure light out put when sq. ft. is a two dimensional measurement?
It's a rule of thumb and accurate enough for our needs, if you want to get serious about it you do need to think 3 dimensional about it and talk in par ratings rather than watts or lumens.

TomStoner Reviewed by TomStoner on . why ? why do we use square feet to measure light out put when sq. ft. is a two dimensional measurement? at the very least we shuold measure it in at least three dimensions being cubic feet considering they way unnatural light wanes in strength the further from the source it is. i suppose that square feet is a decent maesuement of sun light because lumenessence is the same on the ground as it is six feet above so you can say that the entire plant is getting an equivalent amount of light. whereas with Rating: 5