From: Richard Aiken

> (Although I honestly still don't understand why his sunbeam weapon has to have a ceiling on effective damage . . .)

Because no possible arrangement of mirrors can focus sunlight to an intensity greater than the intensity at the surface of the sun (this is true for concentrating light from any surface that emits light in a non-directional manner). If it were possible to do so, all kinds of second law of thermodynamics violations would become practical.