R. Dr. Warren Goldstein on Parsha Ki Tisa, and the glow:
Given Moses' greatness, his glow was no ordinary glow. The rays of light shining from his face were so awe-inspiring that the people were too intimidated to approach him. The Netziv (d. 1893) explains that Moses' face was glowing because he had just come down from Mount Sinai after having spent forty days learning the Oral Torah with the Almighty in order to be able to transmit it to the nation. Moses' face was beaming from the spirituality that comes from the connection with the Divine through the power of learning Torah.
I can personally attest to–among certain holy, righteous people I’ve known–a certain “glow” to their face, something beyond mere human charisma.
(תודה to George Eroes for this link)