30 watts per sq ft is the usual recommendation for LEDs, but some are more efficient than others.
Your lights look like outmoded blurples with white added, and you probably will need 30 watts per sq ft.
Instead of the 600 watts for 20 sq ft, you've got only 370.
With excellent LEDs 25 watts per sq ft works, but those don't look excellent.
Grow style will influence number of plants.
In hydro, even a 2 ft x 2 ft space gives me unhappy plants for lack of elbow room.
For hydro, small autos might be fine in a 2 ft x 2 ft space, but 3 x 3 makes for happier plants.
