Lewis & Short

ēlūcesco, ĕre, 3, v. inch. n. [eluceo], to shine forth, begin to shine (late Lat.), August. Retr. 1, 13: elucesco, παρεκφαινειν, Gloss.
Esp., to dawn: donec dies elucescat, Vulg. 2 Pet. 1, 19.
Impers.: cum jam elucesceret, Vulg. 1 Reg. 9, 26.