What is the origin of the phrase “darkness visible”

Question: What is the origin of the phrase “darkness visible”?

Answer: It appears in Milton’s Paradise Lost (Bk I. 1. 63)

A dungeon horrible on all sides round. As one great furnace flamed yet from those flames No light, but rather darkness visible. Served only to discover sights of woe.

This great work was begun in 1658, when Milton was already blind, and the sombre gloom of these lines may well be contrasted with the many beautiful passages in which the poet was able to conjure up his visions of light, in words which seem to acquire a greater strength and majesty because of the perpetual darkness in which he lived.

The same phrase, “darkness visible”, was used far less effectively, by Alexander Pope, in the Dunciad (Bk lv. 1. 3.) and by Gilbert White, in his Natural History of Selbourne (Letter xxvi)