Saint Thomas Church will webcast the Office of Tenebrae this evening at 5:30; this is always a stunningly beautiful service. [EDIT: That link is from last year, but you can now listen to St. Thomas' 2013 Tenebrae, sung on March 27.]
Here's the service leaflet, in PDF.
This service anticipates the monastic offices for the last three days of Holy Week. Tenebrae means "shadows" and refers to the gradual extinguishing of candles and lights as the service proceeds, until only one candle remains.
As the people enter the church before the service begins, they see in the chancel seven candles glowing brightly. The altar candles, too, are lit, though the candles are made of non-bleached beeswax, just as we use at funerals.
The Order of Service proceeds as follows:
The ministers enter in silence and proceed to their places. Three acolytes, who at almost all other services would be carrying a cross and two torches, walk ahead of the ministers, empty-handed.
The choir and cantors then progress through a series of antiphons and Psalms. At the end of Psalm 69, the first candle is extinguished. At the end of Psalm 70, the second. At the end of the Psalm 74, the third. As each candle is snuffed out, the lights high above the congregation are dimmed a bit more.
Then comes a period where the lights remain as they are: the Lord's Prayer is said, and a series of three lessons and three responsories are sung.
This is followed by the Lauds, another series of antiphons and Psalms during which three more candles are extinguished (after Psalm 63, after the Song of Moses, and after Psalm 150). Now, the nave of the church is very near dark, as the lights have been dimmed even further.
Near the end of the canticle, acolytes emerge to extinguish the altar candles, leaving only the seventh candle lit.
During the repetition of the antiphon after the canticle, the Verger climbs a ladder, removes the candle, and as the choir sings the motet, she takes it toward the High Altar, through the Sanctuary gate, and then hides it in a small room hidden behind the door to the north side of the High Altar.
The congregation says the Lord's Prayer and the choir sings the Miserere.
The Officiant says a prayer and adds (whispering to himself under his breath): "...who liveth and reigneth with thee and the Holy Ghost, ever one God, world without end. Amen.
A loud sound fills the church. Christ is dead. The organ is outraged; the choristers beat their books against their stalls.
Then, in complete silence, the candle emerges from its hiding place. It is returned to its place high above the chancel. By its light all leave in silence.
Officiant: Fr Mead Sung by: The Saint Thomas Choir of Men and Boys Psalms for Tenebrae: Plainsong The Lamentations of Jeremiah: Plainsong Christus factus est: Felice Anerio, (c. 1560-1614) Miserere mei, Deus: Gregorio Allegri (1582-1652)