"Clair de lune" just means 'moonlight.' ('de' is possessive; 'clair' = light). "Enlightenment" in French is also "l'Eclairage" (as in what we call the era after the Dark Ages).
"Au clair de la lune" = Under the moonlight. Like in the well-known French song:
Au clair de la lune
Mon ami Pierrot
Prête-moi ta plume
Pour écrire un mot
Ma chandelle est morte
Je n'ai plus de feu
Ouvre-moi ta porte
Pour l'amour de Dieu.
Etc.