How many Shabbat candles should one light?

Although, strictly speaking, only one candle is sufficient to light for Shabbat, the Shulhan Aruch (O.H. 263:1) says that there is a practice to light two candles, one alluding to Zachor (remembering Shabbat) and one alluding to Shamor (keeping Shabbat). The Magen Avraham (ibid:2) writes of customs to light seven candles, which allude to the days of the week, and even ten candles, to symbolize the Ten Commandments.  The Kaf Hahaim (ibid:10) also mentions the custom of lighting seven candles, but bases it on the teachings of Kaballah. Rabbi Yitzhak Palagi (Yafe Lalev, vol. II, § 3) says that Shlomo Hamelech’s Menora had ten branches, and since the root of his name is “peace”, it is appropriate to light ten Shabbat candles.

The common Moroccan custom is to light two Shabbat candles. Rabbi Mas’ud Abuhatzira, in his Piyut “Mizmor Shir Leyom Hashabbat,” mentions writes “Hova Shete Nerot Tadirim” (lit. “the obligation is to have to constant candles”).  According to Gematria, “Ner” has the value of 500, which equals the amount of limbs in a male (248) and the amount of limbs in a woman (252). 

The Rama (ibid.) writes that if a woman forgets to light the Shabbat candles, she must light three Shabbat candles for the rest of her life as a penalty.  Rabbi Ben Zion Abba Shaul (Or Lezion, ch. 18, § 12) and Rabbi Ovadia Yosef (Hazon Ovadia, vol. I, pg. 174) write that nowadays that there is electricity, this is no longer the case. One of the reasons that the Mitzvah of Shabbat candles was instituted was to provide light such that people to knock into each other in the dark and quarrel. Therefore, even if a woman forgets to light, there are other lights in the home that are on, which provide their own light. Furthermore, Rabbi Ovadia is lenient in imposing the penalty in cases where a woman wanted to light but was caught up in Shabbat preparations and missed the time, or in the case in which a woman eats in someone else’s home Nowadays, the penalty would only be applicable if a woman wantonly ignored the Mitzvah of Shabbat candles. 

Summary:  The Moroccan custom is to light two Shabbat candles. In most cases nowadays, a woman need not light an extra Shabbat candle as a penalty if she failed to light the candles previously.