Minimal Lumens for survival: 2,000 p/sq. ft.
Minimal Lumens for good growth: 5,000 /sq. ft.
Minimal Lumens for Max growth: 7,500 / sq. ft.

Watts are meaningless without factoring lumen AND kelvin temp output of lighting.

Lumens
Kelvin Temp
Distance from Canopy

All work together.

Good Luck.