It's a polically-correct (at that time) revolt against the King and the religion. The word light refers also to the religion (first words of the Bible and the angel of the light).
‘Le siècle des Lumières [plural] … Le terme de «Lumières» a été consacré par l’usage pour rassembler la diversité des manifestations de cet ensemble d’objets [la superstition, l’intolérance, l’abus des Églises et des États].’ (fr.wikipedia.org) — Except for Postmodernism, an era does not usually give itself a name. The term was coined later on (say, just about the acme of the revolution’s Terror, when a cult of such lights/gleams/luminaries was contrived). Where in German it reads ‘Aufklärung’, in French ‘éclaircissement’ is used instead.
First words of the Bible: בְּרֵאשִׁית, בָּרָא אֱלֹהִים, אֵת הַשָּׁמַיִם, וְאֵת הָאָרֶץ. ‘In the beginning God created the heaven and the earth.’ (Gn 1,1) — Okay, the third verse reads, in French (Bible de Sacy translation): ‘Or Dieu dit: Que la lumière soit faite. Et la lumière fut faite.’ — Not a plural.
The angel of the light = Lucifer (<Lat. ‘light-bearer’); cfr 2 Cor. 11:14: ‘And no wonder, for Satan himself masquerades as an angel of light.’ — I don’t believe Kant could ever have imagined him being associated with satanism…
