The Prophet (peace be upon him) is a light that provides the right guidance as Allah says:
And verily, you (O Muhammad صلى الله عليه و سلم) are indeed guiding (mankind) to the Straight Path (i.e. Allâh’s Religion of Islâmic Monotheism).
And He (Exalted be He) says:
O Prophet (Muhammad صلى الله عليه وسلم)! Verily, We have sent you as witness, and a bearer of glad tidings, and a warner,
And as one who invites to Allâh [Islâmic Monotheism, i.e. to worship none but Allâh (Alone)] by His Leave, and as a lamp spreading light (through your instructions from the Qur’ân and the Sunnah - the legal ways of the Prophet صلى الله عليه وسلم).
The Prophet's body is not made of light nor is it part of Allah's Light. He is only formed of flesh and blood as was described in the Qur'an. He was born to human parents like all humans by Allah's Will. He used to eat, drink, and care for his daily affairs. When he was blocking the rays of the sun or any other source of illumination, he had a shadow like all people (i.e. thus he is not light, for shadow follows only opaque objects). As for the saying of Allah:
Indeed, there has come to you from Allâh a light (Prophet Muhammad صلى الله عليه وسلم) and a plain Book (this Qur’ân).
Wherewith Allâh guides all those who seek His Good Pleasure to ways of peace
The purpose meant here is the revelation by which the Prophet was sent. It has not been confirmed in the Qur'an or in the authentic Sunnah (whatever is reported from the Prophet) that the Prophet is the light of Allah's `Arsh, thus, whoever claims this is a liar.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.