Generally candles should not be placed on the credence table.
The exception is for the Stational Mass of the Diocesan Bishop, where putting candles on the credence table is clearly an option:
“129 It is preferable that the processional cross be placed near the altar and serve as the altar cross; otherwise it is put away. The candlesticks are placed near the altar or on a side table or at some nearby place in the sanctuary (chancel).”
(Ceremonial of Bishops, Liturgical Press, 1989, ISBN 0-8146-1818-9, page 52).
For a normal Mass the 2002 General Instruction of the Roman Missal (GIRM) applies. It makes no mention of putting candles on the credence table. It has:
“122. On reaching the altar, the priest and ministers make a profound bow. The cross adorned with a figure of Christ crucified and perhaps carried in procession may be placed next to the altar to serve as the altar cross, in which case it ought to be the only cross used; otherwise it is put away in a dignified place.** In addition, the candlesticks are placed on the altar or near it.**. It is a praiseworthy practice that the Book of the Gospels be placed upon the altar.”
This seems to say that the processional candles are to be the altar candles. It describes the procession and what is to happen with the candles in the procession. Does “near” the altar mean on the credence table? I doubt it.
Similarly in this section from the 2002 GIRM, approved for the USA, which can be accessed from
romanrite.com/girm.html
“*The Articles to Be Prepared *
117. The altar is to be covered with at least one white cloth. In addition, on or next to the altar are to be placed candlesticks with lighted candles: at least two in any celebration, or even four or six, especially for a Sunday Mass or a holy day of obligation. If the Diocesan Bishop celebrates, then seven candles should be used. Also on or close to the altar, there is to be a cross with a figure of Christ crucified.
The candles and the cross adorned with a figure of Christ crucified may also be carried in the Entrance Procession.”
By saying “The candles” is seems to be saying: “The candles for the altar … may be carried in procession.”
Candles can be used when the Gospel is read. Where do they come from? The altar is indicated, because taking the Books of the Gospels from the altar is mentioned along with the lighted candles. From the 2002 GIRM:
“133. If the Book of the Gospels is on the altar, the priest then takes it and goes to the ambo, carrying the Book of the Gospels slightly elevated and preceded by the lay ministers, who may carry the thurible and the candles. Those present turn towards the ambo as a sign of special reverence to the Gospel of Christ.”
Similarly in n. 175: “… The deacon signs himself with the Sign of the Cross and responds, Amen. Having bowed to the altar, he then takes up the Book of the Gospels which was placed upon it. He proceeds to the ambo, carrying the book slightly elevated. He is preceded by a thurifer, carrying a thurible with smoking incense, and by servers with lighted candles. …”.
These candles, for the Gospel, are clearly optional, from the Order of Mass of the Roman Missal: “Then the deacon (or the priest) goes to the lectern. He may be accompanied by ministers with incense and candles.” (Roman Missal, Catholic Book Publishing Co., New York, 1985, page 367). The 2002 Latin edition has “pro opportunitate” indicating that this is optional.
Lighted candles on the credence table give it a prominence that is clearly not intended by this part of the GIRM:
“307. The candles, which are required at every liturgical service out of reverence and on account of the festiveness of the celebration (cf. above, no. 117), are to be appropriately placed either on or around the altar in a way suited to the design of the altar and the sanctuary so that the whole may be well balanced and not interfere with the faithful’s clear view of what takes place at the altar or what is placed on it.”