Hail, gladdening Light

Phos Hilaron (Φῶς Ἱλαρόν) is the earliest known Christian hymn recorded outside of the Bible that is still being used today. Phos literally translated means anything emitting light and Hilaros literally translated is cheerful and joyous. This is a modern translation from John Keble:

Hail, gladdening Light, of His pure glory poured
Who is th’immortal Father, heavenly, blest,
Holiest of Holies–Jesus Christ our Lord!

Now we are come to the sun’s hour of rest;
The lights of evening round us shine;
We hymn the Father, Son, and Holy Spirit divine!

Worthiest art thou at all times to be sung
With undefiled tongue,
Son of our God, giver of life, alone:
Therefore in all the world thy glories, Lord, thy own. Amen.