Light on, or at least in, Book III

Looking back at Book III, one could very well call it the "book of light." It begins with the invocation to light,

Bright effluence of bright essence increate

.and rises to a climax on the source of worldly light:

The golden Sun in splendor likest Heaven

This being Milton, there's more to light than first appears, and we're not bathed in the neutral, evenly distributed fluorescence of the observational laboratory of scientific reason. 

The invocation in Book III addresses primordial holy Light, not the sun. If we think of "light" as a spectrum from the highest holy light to the dimmest light of "darkness visible," we discover that at the high end, we see nothing: God's beam is blinding, even when in a cloud. And material light is not invariably revealing: Satan manages to hide his actual identity from the sharpest-eyed archangel, Uriel, precisely at the brightest spot in creation.

Clearly (no pun intended) Milton is trying to establish light's importance even as he suggests critical ways in which it can fall short. Light does not show us, our eye -- everything we need to see, to understand. We learn of God and the Son's plan to counter Satan's schemes via a difficult, tightly coiled verbal maze of an argument; nearly all of it deals with supersensory concerns, like Justice, Mercy, and Grace.

Light can also lead astray. Satan sees the ladder to Heaven, but is attracted like a moth to the Sun, a shiny new bauble.

All of which is to suggest that there's more to what is going on in Paradise Lost than meets the eye. The power of light to carry or to reveal knowledge, truth, is shown as compromised, less than all-sufficient, fallible. When Uriel describes creation, first comes an act of the word:

I saw when at his Word the formless Mass,
This worlds material mould, came to a heap:
Confusion heard his voice, and wilde uproar [ 710 ]
Stood rul'd, stood vast infinitude confin'd;

One might ask, what was it that he "saw", and how could he see it? Only at the Word's "second bidding" did light cause the world to appear. We're dealing with something more - or other - than purely a solar system.

For the reader, it's perhaps illuminating to sense the reservation, the skeptical brackets, being put around light in the poem. This may resonate more when Lucifer seduces with his promise to enlighten Adam and Eve.