[Al B. Fuct]

A 1000 over a 4'x4' tray does technically fit the rough guide of 50W HPS/sq ft for flowering areas (62.5W/sq ft). However, efficient horizontal light fixtures (notably with batwing reflectors) lay down a rectangular light pattern. If you want to cover a square area, a vertical fixture with a conical reflector would best suit. However, vertical fixtures have some problems. It they're arranged with the socket on the top (as most are), the socket cops a lot of heat, lessening the life of the HPS bottle. Also, vertical fixtures rely on bouncing most of the light off the reflector before it gets to the plants. A direct light path from lamp tube to plants puts the greatest light intensity on the leaves instead of on the reflector.

You're better off with a 3'x ~5' tray space under a 1000 with a horizontal fixture and batwing reflector.