The expression might have originated while in the Gnostic dualism of the forces of Light and Darkness, and a lot of people who claimed to become Illuminati, All those enlightened by a higher knowledge, joined the Rosicrucians and took refuge in France to escape the fires on the Spanish Inquisition. https://illuminatiitanimulli58135.blogdigy.com/illuminati-song-lyrics-for-dummies-42504421