Catholic Encyclopedia (1913)/Lumen Christi
The versicle chanted by the deacon on Holy Saturday as he lights the triple candle. After the new fire has been blessed outside the church a light is taken from it by an acolyte. The procession then moves up the church, the deacon in a white dalmatic carrying the triple candle. Three times the procession stops, the deacon lights one of the candles from the taper and sings, "Lumen Christi", on one note (fa), dropping a minor third (to re) on the last syllable. The choir answers, "Deo gratias", to the same tone. Each time it is sung at a higher pitch. As it is sung, all genuflect. Arrived at the altar, the deacon begins the blessing of the Paschal Candle (Exultet). The meaning of this rite is obvious: a light must be brought from the new fire to the Paschal Candle; out of this the ceremony grew and attracted to itself symbolic meaning, as usual. The triple candle was at first no doubt, merely a precaution against the light blowing out on the way. At one time there were only two lights. The Sarum Consuetudinary (about the year 1210) says: "Let the candle upon the reed be lighted, and let another candle be lighted at the same time, so that the candle upon the reed can be rekindled if it should chance to be blown out" (Thurston, "Lent and Holy Week", 416). A miniature of the eleventh century shows the Paschal Candle being lighted from a double taper (ibid., 419). The triple candle appears first in the twelfth and fourteenth Roman Ordines (P. L., LXXVIII, 1076, 1218), about the twelfth century. Father Thurston suggests a possible connexion between it and the old custom of procuring the new fire on three successive days (p. 416). But precaution against the light blowing out accounts for several candles, and the inevitable mystic symbolism of the number three would naturally apply here too. Durandus, in his chapter on the Paschal Candle (Rationale, VI, 80), does not mention the triple candle. In the Sarum Rite only one candle was lighted. While it was carried in procession to the Paschal Candle, a hymn, "Inventor rutili dux bone luminis was sung by two cantors, the choir answering the first verse after each of the others ("Missale Sarum", Burntisland, 1861-83, 337). In the Mozarabic Rite the bishop lights and blesses one candle; while it is brought to the altar an antiphon, "Lumen verum illuminans omnem hominem", etc., is sung (Missale Mixtum, P. L., LXXXV, 459). At Milan, in the middle of the Exultet a subdeacon goes out and brings back a candle lit from the new fire without any further ceremony. He hands this to the deacon, who lights the Paschal Candle (and two others) from it, and then goes on with the Exultet (Missale Ambrosianum, editio typica, Milan, 1902, Repertorium at end of the book, p. 40).
THURSTON, Lent and Holy Week (London, 1904), 414-17.