I wonder what is the Mekor of the 30 min that hazal instituted for the length of the lighting??
As even after the Zman hazal pasken That we should light for 30 min.
Salomon Amar DDS, PhD.
The Shulchan Aruch (O.C. 672:2) says that the reason for half an hour is that this is the amount of time that people were generally in the streets after nightfall. Since the Persumei Nisa is for the people in the streets, this is how long it was instituted to light. The Mishnah Berurah (672:5) indeed says that after nightfall one would technically only have to use as much oil as would last until half an hour after nightfall (i.e. if he is ten minutes late, only twenty minutes of oil). However, he quotes the Pri Chadash who says that since nowadays we light primarily for the Bnei ha'Bayis (people of the household), one must light for half an hour anyways, even if he lights late at night.
All the best,
So what is the reason for the Pri Hadash to say that although nowadays we light primarily for the Bnei ha'Bayis (people of the household) and there we need only few min for pisum haness ostensibly , one must still light for half an hour anyways, even if he lights late at night.
While the Pri Chadash himself does not explain this, the Aruch Hashulchan (O.C. 672:3) says that half an hour is the amount of time that the candles provide a "Heker" (i.e. Persumei Nisa) for the people of Reshus ha'Rabim when one lights at nightfall. Accordingly, he says, when one lights in a manner that the "Heker" is for the Bnei ha'Bayis, he also requires a "Heker" of half an hour. In other words, Chazal instituted that whenever one lights, he should provide Pirsumei Nisa that lasts one half hour, whether this was in the public domain or in a private domain.
All the best,