The Polyelaios
Polyelaios translates from Greek as “much oil.” It refers to a large chandelier which, in some Byzantine traditions, hangs from the center of the church beneath the cupola. If a polyelaios is present, it often has a large metal ring surrounding it called a horos/choros or corona.
There is some variation on which saints are depicted in icons that go around the corona, but one common example is Old Testament saints facing inward toward the light and New Testament saints like the apostles facing out toward the people.
St. Sophia has a 3-tier chandelier, or polyelaios, which hangs over the tetrapod at the front of the nave.

Metropolitan Vitaly, 1988

Candles appeared in all Orthodox churches in the first centuries of our era. Eusebius of Caesaria records that during the paschal vigil such a quantity of candles were lit by the faithful that the night itself became as day. There were wax candles the sizes of which made them look like actual pillars. In answer to the accusations of the schismatic Vigilantius, who berated the Orthodox for lighting candles in their churches during daylight also, St. Jerome (342-420) says “in all Eastern churches candles are lit during the reading of the Gospel not only so as to shed light and dispel the gloom but also to proclaim one’s joy.”
Over the centuries, the Orthodox candle has burnt gently and humbly and is now, as it was then, imbued with profound meaning, inalienable from our Orthodox divine services and Orthodox piety. Apart from the fact that the small sacrifice, the mite given by each Christian for the candle he lights, benefits the Church in real terms, by lighting a candle, each Christian enters into closer contact with the church and the service, participating in it more actively and invisibly warming his soul by the visible light of the candle. We must understand that man’s immortal soul dwells in man’s mortal body.
The immortal soul cannot be indifferent to pious deeds committed by the body which is its home. As the body bows, so does the soul bow with it and grows obedient. We are human; we need to see, to feel, to smell and to hear. And in the church, candles burn with the divine light; the ringing of bells sanctifies the air; incense reminds us of the fragrance of prayers; and from each icon the Saviour Himself, the Mother of God and all the saints mysteriously look at us and we look at Their holy images as two worlds come face to face: the dwellers of the Kingdom of God and we, the sinners.
Pious Orthodox people will preserve throughout the year the candles they light during the readings of the Passion Gospels on Holy Thursday. They make a sign of the cross with these candles over the doors to their homes. They light them during difficult moments of their lives. On Easter night, the candles burnt by the faithful transform their faces into living icons on which plays the light of God’s grace…
But the candle has yet another profound meaning. The burning candle represents the entire life of the faithful, from birth to death. It stands for the inner flame of love for and devotion to God. A Christian should burn like a candle before God, and his whole being should gradually be consumed by this divine flame thus marking the end of his earthly life.

Why Are Vigil Lamps Lit Before Icons?
by Bishop Nikolai of Ohrid and Žiča in the Prologue of Ohrid

First – because our faith is light. Christ said: I am the light of the world (John 8,12). The light of the vigil lamp reminds us of that light by which Christ illumines our souls.
Second – in order to remind us of the radiant character of the saint before whose icon we light the vigil lamp, for saints are called sons of light (John 12,36; Luke 16,8).
Third – in order to serve as a reproach to us for our dark deeds, for our evil thoughts and desires, and in order to call us to the path of evangelical light; and so that we would more zealously try to fulfill the commandments of the Saviour: “Let your light so shine before men, that they may see your good works” (Matthew 5,16).
Fourth – so that the vigil lamp would be our small sacrifice to God, Who gave Himself completely as a sacrifice for us, and as a small sign of our great gratitude and radiant love for Him from Whom we ask in prayer for life, and health, and salvation and everything that only boundless heavenly love can bestow.
Fifth – so that terror would strike the evil powers who sometimes assail us even at the time of prayer and lead away our thoughts from the Creator. The evil powers love the darkness and tremble at every light, especially at that which belongs to God and to those who please Him.
Sixth – so that this light would rouse us to selflessness. Just as the oil and wick burn in the vigil lamp, submissive to our will, so let our souls also burn with the flame of love in all our sufferings, always being submissive to God’s will.
Seventh – in order to teach us that just as a vigil lamp cannot be lit without our hand, so too, our heart, our inward vigil lamp, cannot be lit without the holy fire of God’s grace, even if it were to be filled with all the virtues. All these virtues of ours, after all, like combustible material, but the fire which ignites them proceeds from God.
Eighth – in order to remind us that before anything else the Creator of the world created light, and after that everything else in order: And God said, let there be light: and there was light (Genesis 1,3). And it must be so also at the beginning of our spiritual life, so that before anything else the light of Christ’s truth would shine within us. From this light of Christ’s truth subsequently every good deed is created, springs up and grows in us.
May the Light of Christ illumine you as well!