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CHICAGO — As the sun rises, the glowing lights in the huge rooftop greenhouse dim.

Here, lettuce never sleeps.

It grows, quickly — much more quickly than it would in a farm field. And there is a lot of it, as well as other types of salad greens and herbs. This greenhouse atop a soap factory in Chicago’s historic Pullman neighborhood is enormous.

Its owners, New York-based Gotham Greens, claim there is no bigger rooftop greenhouse in the world.

“It’s hard to picture what a 75,000-square-foot greenhouse really feels like when you’re in it,” says Viraj Puri, CEO and co-founder of Gotham Greens, “It’s about two acres, a couple football fields.”

The facility will produce leafy greens year-round for customers including local restaurants and grocery stores.