What is the ruling on describing the Prophet, peace and blessings be upon him, as "light upon light"?

The Prophet, peace and blessings be upon him, is a light, as Qatadah explained the verse, "There has come to you from Allah a Light and a clear Book," by saying that the Light is Muhammad, peace and blessings be upon him. This is further indicated by Allah's description of him: "Indeed, We have sent you as a witness and a bringer of good tidings and a warner, and one who invites to Allah, by His permission, and an illuminating lamp." As for describing him as "light upon light," there is no evidence to support its legitimacy.