We sing this as part of vespers and also during the Liturgy of the Presanctified Gifts during Lent. Both the words and the melody are hauntingly beautiful, and it's a beautiful song of praise focusing on God.
I realize the song was originally written in Greek, but I love the English translation we use. Just the word "gladsome" sends chills down my spine. And I love the archaic phrase "for meet it is at all times." And I love the idea of the "light of evening." I believe it's talking about the wonderful time of twilight, when the light takes on a mystical, otherworldly essence.
Most of all, I love the way the song draws our focus toward God and not ourselves.
Here are the words we use in our church:
O Gladsome Light of the holy glory of the Immortal Father, heavenly, holy, blessed Jesus Christ. Now we have come to the setting of the sun and behold the light of evening. We praise God: Father, Son, and Holy Spirit. For meet it is at all times to worship Thee with voices of praise, O Son of God and Giver of Life, therefore all the world doth glorify Thee.
There are many melodies used, but this one comes closest to the one we sing in our church: