The answer depends entirely on the size of the plants! The number of plants that can be grown under a light is the number that would fit in the appropriate flowering or vegetative footprint we specify for the light model. Most commonly-grown plants can be maintained at different sizes through pruning, and the size of determinate plants (those which die after flowering) is dictated by the size they were when flipped into flower, so there is no standard number of plants that will fit in any given area-- it is all about how big you want to grow them!