Is it forbidden to do "work" after Shabbat candle lighting time?

In most communities, candle lighting time is eighteen minutes before sunset. Although work is not forbidden until sunset, at which time Shabbat officially enters, it is established custom not to delay the candle lighting until the last possible moment, for fear that something may crop up at the last minute, or that one may then light too late, and thus, G‑d forbid, desecrate the Shabbat.

Although Shabbat enters at sunset, one has the prerogative of accepting the Shabbat up to one and a quarter "seasonal hours" (see Hours for the definition of this term) before sunset. After a person ushers in the holiness of Shabbat, although it is still "weekday" for all others in the vicinity, that person is precluded from doing any activity that is forbidden on Shabbat.

So the question now is: does lighting Shabbat candles constitute acceptance of Shabbat for the individual who has kindled? Is a person who lit Shabbat candles automatically forbidden from doing work, although it is before sunset?

The halachic authorities disagree on this, and the Code of Jewish Law follows the lenient position. Nevertheless, it has become standard practice (and as such it attains the full strength of Jewish law) for women to accept Shabbat with the kindling of Shabbat candles, unless the woman specifically had in mind while lighting the candles that she wishes to delay the acceptance of Shabbat for a short period of time.1

However, men have never accepted upon themselves this stringency. Therefore, in an instance where a man lights the Shabbat candles (such as when there is no adult woman present), he may continue doing all forms of work until the Shabbat actually enters with sunset.

I'd like to add two notes:

a) Though lighting candles doesn't constitute an acceptance of Shabbat (for men, and for women who have in mind not to accept Shabbat at the time), the recitation of the Friday night Shabbat prayers (which also may be done before sunset, see More on Plag Hamincha) does constitute an absolute acceptance of Shabbat.2

b) We are required to "add" on to Shabbat, both when it enters and when it departs. This means that we may not do work until the moment of sunset (or the moment that three stars appear on Saturday night), but we must accept the holiness of Shabbat at least a few moments beforehand.

Shabbat Shalom!

Yours truly,

Rabbi Naftali Silberberg,
Chabad.org Editorial Team