If a woman or girl forgets to light Shabbos candles, there is a Knas, a penalty, that she must light an additional candle from the following week onwards. There are many discussions In Poskim about this Halacha: 1. In a case where the forgetfulness is considered to be an absolute accident or for a reason beyond her control; 2. There is a discussion about whether the same rule applies if she forgot to light candles on a Yom Tov; 3. If she forgot to light the same number of candles that she normally lights and diminishes their number; 4. If there is electrical lighting that illuminates the home anyhow; 5. and other similar questions. In any case where there is a question whether there is a Knas to light an additional candle from the following week onwards or maybe only the following week, a Rov should be consulted as to the details.