Phos Hilaron

Phos Hilaron (Φῶς Ἱλαρόν) is an ancient Christian hymn originally written in New Testament Greek. Often referred to by its Latin title Lumen Hilare it has been translated into English as 'Hail Gladdening Light' or 'O Gladsome/Joyous Light'. It is the earliest known Christian hymn recorded outside of the Bible that is still in use today. The hymn is part of vespers in the Eastern Orthodox Church, and also included in some modern Anglican and Lutheran liturgies.