The elaborating clause here is a paraphrase of Diogenes Laertius 2.9, where it is presented as an opinion of Anaxagoras (cf. Diels-Kranz 59 A42; on Anaxagoras see alpha 1981). Long and Markovich, in their editions of D.L., adopt emendations of Aldobrandinus and von der Mühll that change the meaning significantly from the rather opaque statement found here: "a reflection of the light of the stars that are not being shined on by the sun." This reading is confirmed by reflections of the same source in Hippolytus, Against All Heresies 1.8.10 (D.-K. 59 A42), and, independently, at Aetius 3.1.5 (D.-K. 59 A80). LSJ entry at web address 1.