During Holy Week, a candle triangle is traditionally used during Matins and Lauds and Holy Mass.
From the Maundy Thursday liturgy in the Liber Usualis:
At the end of each Psalm of Matins and of Lauds, one of the 15 candles is extinguished on the triangular candlestick before the altar, the candle at the top being left lighted.
(Then follows many pages of chants for Matins and Lauds.. After Traditor autem dedit eis signum... the following is provided..)
Fourteen of the candles on the triangular candlestick having been extinguished as has already been explained, the one at the top of the triangle alone remains lighted. During the Canticle Benedictus, the six candles on the altar are likewise extinguished one by one, from each side alternately, at every second verse, so that by the last verse all are extinguished. All other lights and lamps in the church are also put out. During the repetition of the Antiphon Taditor, the lighted candle is taken from the top of the candlestick and hidden behind the altar at the Epistle side.
There is no other time in the Liturgical year where there is so many differences in the daily and weekly norm of what happens at Mass, as during the Triduum of Holy Week. This USED to be from Maundy Thursday morning to Easter Sunday morning, but one of the changes that came with Bugnini was to move that to Thursday EVENING and extend it to Sunday EVENING. Why? No reason was ever given, like the other numerous changes: no good reason was ever given -- it was change for the sake of change, ostensibly because change is good.
Keep in mind, that the wreckovation foisted upon the Church in the name of the (unclean) "spirit of Vatican II" began with tampering with Holy Week, and it happened under the watch of Pope Pius XII. He appointed the Freemason Anibale Bugnini to his position of power in the newly established office of Liturgical Reform, as its Secretary. One change after another came down the pike, and after about 1954, change became the norm. Nobody knew what wild innovation was going to be demanded of them from one day to the next. Everything was in 'FLUX' as the ancient philosophers would say.
It is a spirit of worldliness that demands updating, new models, renovation, remodeling, renewal, reform and change. To "keep up with the Joneses" you have to have the latest model of car and the newest style of clothing. So Newchurch is trying harder to keep up with the Lutherans and the Pres-byterians than it is trying to hang on to Sacred Tradition.
It's out with the old and in with the new. So don't be surprised if you find that it's hard to learn what candles are for. We use electric candles now, don'tcha know? You put a quarter in the slot and push a button and the flickering electric imitation flame lights up, and your insurance premiums go down.
You're making money! Must be doing SOMETHING right!