Q. Is it obligatory to light six candles for a Sunday mass?
A. No, but the sense of the law is that an increased number of candles shows a celebration of greater importance. Here’s GIRM 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 Holyday of Obligation, or if the Diocesan Bishop celebrates, then seven candlesticks with lighted candles.”