Our Sages give several reasons for the lighting of Shabbat and holiday candles. The two primary reasons are:
1) A setting that encourages stumbling in the darkness is not conducive for the calm and peace that befits the holy Day of Rest.
2) The light of the candles adds to the peaceful ambiance. They demonstrate respect for the holy day, and sustain the atmosphere of oneg (pleasure) that is supposed to define Shabbat.
All candles and oils are kosher for use as Shabbat candles, even if they contain non-kosher (for eating) ingredients. The candles should be large enough to burn until after nightfall; ideally, they should burn until after the Friday night meal has concluded.
The mitzvah of Shabbat candles actually extends to the entire home (other than the sleeping areas)—stumbling in the kitchen is no less peace-shattering than stumbling in the dining room. But electric lighting is sufficient for all the rooms – kitchen, living room, hallway, bathroom, etc. – other than the room where the Shabbat meal will be held, which should be illuminated by candles (in addition to any electric lights one wishes to leave on). Electrical lighting is not a substitute for the soft glow of the candles and the pleasant mood they create. An electric light should only be used in the eating area in places where maintaining an open flame is not possible, such as a hospital room. (In such a situation, the candle-lighting blessing should be recited before switching on the lights.)
The mitzvah to light Shabbat and holiday candles applies to men and women equally. Yet our Sages instituted that the woman of the home should light the candles for the entire household. If she is not home that weekend or if a man lives alone, the man should kindle the candles. If there is an unmarried daughter at home, then the father should light two candles, and the daughter should light her customary one. If there's a married woman in the home, she can light the candles; the man need not do so.
The Sages give several reasons why ideally the woman of the house lights the candles:
1) The woman of the house is the one normally in charge of all that happens in her home—including ensuring that the house is properly lit.
2) The woman is the one who sets the foundation of every Jewish home. It is the woman's primary task to ensure that the home is a domicile where light, peace, and harmony prevail, suffusing it with an atmosphere conducive for spirituality and G‑dlinesss.
3) "The candle of G‑d is the soul of Man." Eve had a hand in bringing death – the extinguishing of the G‑dly candle – into this world, when she convinced her husband, Adam, to eat from the Tree of Knowledge. To compensate for this, the responsibility of lighting the candles was handed to the woman.
The woman of the home lights candles and technically, the entire household – husband, sons, daughters – is covered. A woman's candle-lighting also covers guests who will be eating together with the family and are sleeping in the same home, such as in a guest bedroom. The custom, however, is for every woman and girl, household member and guest alike, to light her own candle (candles, if post-marriage), starting from the age when she can recite the blessing.
The lighting of the woman of the home does not cover guests who have their own designated living quarters, i.e., a suite with self-sufficient living space. Such guests should light their candles in their own quarters—even if they are joining the host family for the meal.
Guests who will be joining the family for the Shabbat meal, but will not be sleeping in the same home, should light Shabbat candles in the home where they will be sleeping.
There are three exceptions to this rule. If any of the following conditions apply, then the guests should light candles in the home where they will be eating:
1) If by the time the guests return to their own quarters after the meal, their candles will have gone out.
2) If it is necessary for the guests to drive before Shabbat to the home of their hosts. (It is better to light at the host's home than to avail oneself of the option outlined below, of mentally making a condition that one does not accept Shabbat with the lighting of the candles.)
3) If leaving the candles at home unattended poses a fire hazard.
Strictly speaking, one candle is enough to fulfill the mitzvah. The custom, however, is to light two candles, corresponding to the two instructions in the Torah regarding Shabbat: 1) "Remember the day of Shabbat to sanctify it." 2) "Observe the day of Shabbat to sanctify it."
There are those who observe the custom of lighting an additional candle upon the birth of each child—to "illuminate" each child's mazal. Thus a woman with three children would light five candles.
Until marriage, the custom is that women and girls light one candle.
The candles should be set up in a place where the wind will not blow them out, e.g., not near an open door or window.
If the candlesticks are placed on the table, the challah bread or a prayer book should be placed on the table before the candle lighting and should not be removed until nightfall. Otherwise, the table may not be moved for the duration of that Shabbat.
Obviously, for safety reasons, the candlesticks should be stable and be placed on a steady surface, not next to a wall, curtains or the like.
Preparing the Candles
In preparation for candle lighting, some have the custom to light the candles and extinguish them, thus charring the wicks and making it easier to light the candles at the time of the actual lighting. In many households, the man of the house does this, in addition to setting up the candlesticks and candles, thus taking part in this special mitzvah.