That's incorrect. It has nothing to do with the wavelength of the light. > Still the reflected light has original wavelength of the light of the Sun. Collect e

That's incorrect. It has nothing to do with the wavelength of the light. > Still the reflected light has original wavelength of the light of the Sun. Collect enough of it and that triggers fire. You can't collect enough of it into one place with a passive optical system, because it's been irreversibly scattered by the moon's surface (Read: irreversible increase of https://en.wikipedia.org/wiki/Etendue https://en.wikipedia.org/wiki/Etendue).