"This hymn has frequently been ascribed to St. Ambrose, but it is not assigned to him by the Benedictine editors, or by Biraghi in his Inni sinceri e carmi di Sant' Ambrogio, 1862. It is certainly ancient, and may possibly be as old as the 5th cent." —"Jam lucis orto sidere," by James Mearns in A Dictionary of Hymnology, (ed.) by John Julian (1892)