סימן עה סעיף ד
כְּבָר יָדוּעַ שֶׁכָּל הַמִצְוֹת מְבָרְכִין עֲלֵיהֶם עוֹבֵר לַעֲשִׂיָתָן. אֲבָל בְּהַדְלָקַת הַנֵּרוֹת לְשַׁבָּת, כֵּיוָן שֶׁבְּהַדְלָקָה מְקַבֶּלֶת הָאִשָּׁה שַׁבָּת עַל עַצְמָהּ, וְהַבְּרָכָה הֲרֵי הִיא הַתְחָלָה לַהַדְלָקָה, וְאִם כֵּן אִם תְּבָרֵךְ תְּחִלָּה, לֹא תוּכַל עוֹד לְהַדְלִיק, עַל כֵּן הִיא מַדְלֶקֶת תְּחִלָּה. וּכְדֵי שֶׁתְּהֵא הַבְּרָכָה עוֹבֵר לַעֲשִׂיָּתָן, פּוֹרֶשֶׁת יָדֶיהָ כְּנֶגֶד פָּנֶיהָ שֶׁלֹּא תִרְאֶה הַנֵּרוֹת, וּמְבָרֶכֶת וּמְסִירָה אֶת הַיָּדַיִם וְרוֹאָה אֶת הַנֵּרוֹת, וַהֲוֵי כְּאִלּוּ בֵּרְכָה קֹדֶם הַהַדְלָקָה. (וּמִשּׁוּם לֹא פְּלוּג, נוֹהֲגוֹת כָּךְ גַּם בְּיוֹם טוֹב). וְעִקַּר הַנֵּרוֹת שֶׁבָּהֶן הֲוֵי קַבָּלַת שַׁבָּת, הֵן אֵלּוּ שֶׁעַל הַשֻּׁלְחָן שֶׁאוֹכְלִין עָלָיו, וְעַל כֵּן תַּדְלִיק אוֹתָן בַּאַחֲרוֹנָה. וּבִשְׁעַת הַצֹּרֶךְ, כְּגוֹן שֶׁהִיא צְרִיכָה לָלֶכֶת לַטְּבִילָה אוֹ לַחֻפָּה, אוֹ לִשְׁאָר דָּבָר נָחוּץ, תּוּכַל לְהַתְנוֹת שֶׁאֵינָהּ מְקַבֶּלֶת שַׁבָּת בַּהַדְלָקָה (עַיֵן לְקַמָּן ק"ס סָעִיף ה'), וְאָז תּוּכַל לְבָרֵךְ קֹדֶם הַדְלָקָה. וַאֲפִלּוּ תְּנַאי בַּלֵּב, סַגֵּי.
It has already been established that the berachah for all mitzvos must be said before doing the mitzvos. But [this does not apply to] lighting Shabbos candles, for by lighting the candles the woman ushers in the Shabbos; and since the berachah is the beginning of the lighting, if she makes the berachah first she will no longer be able to light the candles. Therefore, she first lights the candles, and in order that the berachah be said before doing [the mitzvah], she covers her face with her hands so that she doesn't see the candles and she says the berachah and removes her hands, and looks at the candles. In so doing, it is like saying the berachah before lighting the candles. (And in order not to differentiate, this procedure is also practiced on Yom Tov.)15Derech Hachaim rules that when a man lights Shabbos candles, he should do it the same way as a woman even though he does not welcome the Shabbos at that time. This is in order not to differentiate in the way we perform the mitzvah. Rabbi Akiva Eiger rules that on Yom Tov the berachah is said before lighting the candles. The important candles with which the Shabbos is welcomed—are those that are on the table where the meal is served, and therefore she should light them last.16Magein Avraham rules the berachah should be said over the candles that are on the table. However, the berachah may also be recited when they are lit in any place that the household will occupy and use. And in time of need, as when she has to immerse herself in the mikvah, or go to a marriage ceremony, or for other important matters, she may light them with the stipulation that she is not assuming [the holiness of] Shabbos with the lighting (of the candles) and then she can say the berachah before lighting. In this regard, even a mental reservation is sufficient.
תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן העולם הבא שנאמר הליכות עולם לו אל תקרי הליכות אלא הלכות (נדה ע"ג.)