Explain how the following contrasting images play against another light - dark?

This is very much an essay question but I can give you a few ideas. The society created by the state is generally dark. It is literally the dark ages of thought. People live under a cloud of ignorance and superficiality. The light comes when we see people like Clarisse who represent an enlightened point of view.

Her face, turned to him now, was fragile milk crystal with a soft and constant light in it"

This is juxtaposed with the darkness of Montag's job as fireman.

They and their charcoal hair and soot-colored brows and bluish-ash-smeared cheeks where they had shaven close.