The “frozen tundra” is a myth. The ground at Lambeau Field, legendary home of the Green Bay Packers, is heated. It has not been frozen during a football game since it was dubbed the “frozen tundra” more than 40 years ago.

And that impossibly green grass these days, despite the calendar turn to January? Trace it, in large part, to a new system of artificial lighting employed to counter the meek late-autumn sunshine in Wisconsin.

Green Bay’s famed “frozen tundra,” besides being redundant — tundra is, by definition, frozen — is downright tropical, even during the N.F.L. playoffs.

“It’s just like playing in the summer on the grass,” Green Bay offensive lineman T. J. Lang said. “It’s never hard, it’s never frozen.”