Hacham Ovadia Yosef, in his Hazon Ovadia Shabbat (p. 215; listen to audio recording for precise citation), writes that it is proper for women before they light Shabbat candles to shut off the electric lights in the room where the Shabbat candles are lit. If the lights are on when a woman lights the Shabbat candles, she will be reciting a Beracha over an insignificant addition of light in the room, and it is Halachically questionable whether this slight addition of light warrants the recitation of the Beracha, "Lehadlik Ner Shel Shabbat." Therefore, Hacham Ovadia rules, it is proper for women to turn off the electric lights, and then recite the Beracha, having in mind both the candles and the electric lights. After reciting the Beracha, they should light the candles and then turn the lights back on. If a woman follows the view of the Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909) that the candles should be lit before the Beracha is recited, then she should turn off the electric lights, light the candles, turn the lights back on, and then recite the Beracha.
This is a very important Halacha, as many women are unaware that the electric lights in the room should preferably be off when the Shabbat candles are lit.
Hacham Ovadia adds that although this method should be followed on an ordinary Friday evening, it is obviously not suitable when Friday is Yom Tob. Women of course light Shabbat candles on Friday afternoon even when Friday is Yom Tob, but it is forbidden to turn electric lights on or off on Yom Tob. Therefore, Hacham Ovadia recommends that when Yom Tob falls on Friday, one should set the electric lights on a timer before Yom Tob so they are turned off at the time of the Shabbat candle lighting, and then go back on afterward. This way, the woman can light the Shabbat candles with the electric lights turned off, without violating Yom Tob.
Summary: It is proper for a woman before lighting the Shabbat candles to turn off the electric lights in the room where the Shabbat candles are lit, so that the candles are lit in a dark room and provide significant illumination. She may then turn the lights back on after lighting the Shabbat candles. When Friday is Yom Tob, it is proper to set the lights in the room on a timer before Yom Tob so they are turned off at the time of the Shabbat candle lighting.
