One of the Berachot that we recite as part of the Habdala service on Mosa’eh Shabbat is "Boreh Me’oreh Ha’esh" – the Beracha over fire. The Shulhan Aruch rules (Orah Haim 298) that one may not recite this Beracha until he derives some benefit from the light of the flame. Specifically, one must receive enough light from the candle that he could distinguish between two coins of different currencies. For this reason, there is a custom from the time of Ge’onim (recorded by the Meiri) to lift one’s fingers toward the flame before reciting the Beracha of "Boreh Me’oreh Ha’esh" to see if he can distinguish between the nail and the flesh. This serves as a "test" to determine whether or not one derives enough benefit from the fire to allow for the recitation of the Beracha.
Often, when Habdala is recited in the synagogue or in other large gatherings, those standing far away from the candle do not derive any benefit from the light of the flame. If a person stands too far from the candle to derive the required amount of benefit, then he does not fulfill this obligation, even though he listened attentively to the Beracha. In such a case, he would have to repeat the Beracha of "Boreh Me’oreh Ha’esh" over a candle upon returning home. Although he has fulfilled the requirement regarding the other Berachot of Habdala, he has not fulfilled the obligation of "Boreh Me’oreh Ha’esh" and he must therefore recite the Beracha over a candle at home.
It is therefore proper when Habdala is recited in a large room – such as in the synagogue – to turn out the lights before the recitation of the Beracha of "Boreh Me’oreh Ha’esh," so that everyone will derive benefit from the light of the candle. And even then, some people standing far away from the candle may not necessarily derive enough benefit from the light, and would thus have to recite the Beracha over a candle at home.
Summary: The Beracha of "Boreh Me’oreh Ha’esh" is recited only if one receives enough light from the flame that he derives some sort of benefit from it. If one hears Habdala in the synagogue or another large gathering, and does not receive light from the candle, he should recite the Beracha over a candle upon returning home.
