actually it will grow more.
because the 'one square foot' is TALL...as tall as you want it to be.
the lettuce is stacked...one on top of the other.
The Solar cells are on the outside.
the LED are calibrated to provide the exact TYPE of light that best suits the vegatable in question.
PLUS
the growing season is 24/7/365.
it's happening.
you must have missed that part when you watched the video.
RE: How Much Land does it take To provide enough food