Estelle Haan, '"Heaven's Purest Light": Milton's Paradise Lost 3 and Vida' *Comparative Literature Studies* 30:2 (1993), pp. 117:

"Hitherto there has been no consensus among scholars about the precise nature of the Light invoked in Book 3. … Sewell identifies it as the Son of God, finding a general parallel in the “living light” of Dante, Paradiso xiii 55, which shines from its source in such a way that it is not disunited from it or its interconnected love. Others, for example Kelley, view it as entirely physical, while Williams and Allen regard it as both physical and divine, arguing that Milton, like Plato, sees Light as the symbolic manifestation of God."

If the bell inscription has any purchase at all on this question, I guess I'm siding with Sewell.