Here is a bit of a blog a pastor friend of mine wrote. (here is the full post) and (here is another post)

"Tonight is the Wednesday night of Holy Week. In the Anglican world, this often means it is time for Tenebrae (a Latin word meaning “shadows” or “darkness”).

Tenebrae is a traditional service that comes from the Benedictine monasteries of Europe. It is a time of experiencing the last week in Christ’s life through psalms, lessons, prayers, and gathering darkness. The centerpiece of the service is a gathering of fifteen candles which are snuffed out, one by one, as the service goes on. This increases the physical darkness, while also symbolizing Jesus’ life ebbing away. 

— A excerpt from the blog of Fr. Thomas McKenzie