Enough light?

I recently bought some used equipment. It included a flowering setup consisting of the following: six 3′ x 3′ ebb-and-flow trays, two 1000-watt and one 400-watt HPS lamps, and a rotating light mover. The six trays are arranged in two rows of three spaced about 8″ apart. From reading your column, my calculations show that 2400 watts over 63 square feet (7′ x 9′ = 63 square feet) is under-illuminated with about 38 watts of light input per square foot. Would it be better to use less space with the same power to improve my power/area?
Santa Cruz, California

With an input of 38 watts per square foot the flowers will not be as large, dense or potent as they would be under a more intense light. Your idea of eliminating two of the six trays seems sound.

Place the four trays in a square configuration. The trays cover between 36 and 49 feet depending on how closely together they are placed. At 36 square feet (11 square meters) the garden has a light input of about 66 watts per square foot. If there is a foot distance between each tray, the garden measures 49 square feet (15 square meters) the light input will be 49 watts per square foot. Obviously, keeping the 4 trays close together so the plants receive the brightest light is the most efficient use of the light.

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