As said earlier, Superman is given his powers from Earths yellow sun, but under a red sun radiation Superman is reverted to mortal stature. In Superman: Red Son, a three issue storyline exploring what would have happened had the infant Kal-El landed in the Soviet Union, President Lex Luthor teams up with Batman to trap Supes in a radiation chamber designed to sap the heros powers. Superman would have been beaten to a pulp had Wonder Woman not freed him from his confinement. The Nineties animated Superman series explored this vulnerability as well, with Brainiac using a red sun lamp to inhibit the Man of Tomorrows powers and keep him trapped in his collection. Although the red sun doesnt neccasarily defeat Superman, it enables pretty much anyone to attack him as if he were a weak human being. This makes it one of the most innovative and interesting ways that Superman has been bested in comics and on TV.