Where does that notion of the mens (reason, spirit) as a light come from? Mens equals lux equals lumen aeternum? This notion was derived by Peucer from Marsilius Ficinus, who himself had originally taken it from the Hermeticum.
Jung directly interrogates the identification of mens with eternal light, tracing the concept from the Corpus Hermeticum through Ficino to early modern dream theory, establishing the Hermetic-Neoplatonic genealogy of the term.
, Dream Interpretation Ancient and Modern: Notes from the Seminar Given in 1936-1941, 2014thesis