I've noticed Luthor's physique tends to vary from creative team to creative team. Sometimes he's portrayed somewhat on the chubbier side, like in this story. But other times he's portrayed as fit and trim, sometimes even muscular, taking as much pride in his physical appearance and fitness as he does in his intellect. (Even though he knows he can't beat Superman, PG or other super-powered types through bare-knuckled fighting alone.)
All of which is to say, I could see the red sunlamp trick giving Luthor a real advantage against PG, Superman or others, if he actually were as strong and fit as some creators portray him. He'd still lose in the end, of course, but he might well temporarily get the upper hand and knock a Kryptonian out.