'''Phos Hilaron''' (Φως ΙλαρόνΦῶς ἱλαρὸν) is an ancient [[Christian]] [[hymn]] originally written in [[Koine Greek]]. The hymn is known in English as ''''Hail Gladdening Light,'''' or ''''O Gladsome Light.'''' It is the earliest known Christian hymn, recorded outside of the Bible, that is still being used today. The hymn is featured in the [[Vespers]] of the [[Orthodox Church]].

The song is first recorded by an unknown author in the ''[[Constitutiones Apostolicae]]'' which was written in the late 3rd or early 4th century A.D. It is found in a collection of songs to be sung in the morning, in the evening, before meals, and at [[candle ]] lighting. Phos Hilaron is to be sung at the lighting of candles in the evening and so is sometimes known as the ''''Candle-light Hymn''''. Despite some of the words to the other three songs being from Scripture or in one case dated to around 150 AD, ''Phos Hilaron'' is the first to be considered an actual hymn in the modern sense. It is certainly the first complete example. It is far more rhythmic than the others and is divided into twelve verses varying between five, six, eight, nine, ten and eleven syllables a verse. [[Basil the Great]] (ca. 330 - [[January 1]], 379) spoke of the singing of the Phos hilaron Hilaron as a cherished tradition of the [[church]], the hymn being already considered old in his day (though some attribute the composition of the song to St Basil himself).

[[Athenogenes]], a [[saint]] of unknown date but whose saint's day is commemorated 16th July, is believed by some to have composed this hymn on the way to being [[martyr]]ed. He is often depicted as an elderly [[bishop]] with the executioner's arm paralyzed until the saint has completed his song. The ''[[Roman Martyrology]]'' states: "In Pontus, the birthday of Saint Athenogenes, [is celebrated, he was] an aged theologian, who, when about to consummate his martyrdom by fire, sang a hymn of joy, which he left in writing to his disciples." He is probably identical to the bishop who suffered at Sebaste, Armenia, with ten disciples under Diocletian on [[July 16]]; therefore estimating his death as around 305 A.D.

St. [[Sophronius I of Jerusalem]] (634-638 A.D), who was known for his poetry, is believed to have revised the hymn.

Φώς 'ιλα�?όν αγίας Φῶς ἱλαρὸν ἁγίας δόξης αθανάτου Πατ�?ός, ου�?ανίουἀθανάτου Πατρός, αγίουοὐρανίου, μάκα�?οςἁγίου, Ιησο�? Χ�?ιστέμάκαρος, ελθόντες επί τήν ηλίου δ�?σινἸησοῦ Χριστέ, ιδόντες φώς εσπε�?ινόνἐλθόντες ἐπὶ τὴν ἡλίου δύσιν, υμνο�?μεν Πατέ�?αἰδόντες φῶς ἑσπερινόν, Υιόνὑμνοῦμεν Πατέρα, καί άγιον Πνε�?μαΥἱόν, καὶ ἅγιον Πνεῦμα Θεόν. Ἄξιόν σε ἐν πᾶσι καιροῖς, Αξιόν σε εν πάσι και�?οίς υμνείσθαι φωναίς αισίαιςὑμνεῖσθαι φωναῖς αἰσίαις, Υιέ Θεο�?Υἱὲ Θεοῦ, ζωήν ο διδο�?ςζωὴν ὁ διδούς, διό ο Διὸ ὁ κόσμος σέ σὲ δοξάζει.