“The phrase “Infunde Lumen Cordibus” (“Shed Thou Thy beams within our hearts”) is best-known from a hymn, ascribed to St. Ambrose and used for Sunday Vespers. St Ambrose’s title was “O lux beata Trinitas” (“O Trinity of Blessed Light”), but it appears in the Roman Breviary under the title “Iam sol recedit igneus” (As fades the glowing orb of day”). St. Ambrose is often credited...