The Mitzvah of Lighting Chanukah Candles
There is a Mitzvah to light Chanukah candles throughout all eight nights of Chanukah (beginning from next Sunday night). The Sephardic custom is to light one set of Chanukah candles per house. The Ashkenazi custom, however, is that every member of the household lights their own Chanukah candles.
The Amount of Oil
When lighting Chanukah candles, one should be certain to put in enough oil so that they will remain lit for at least half an hour from the initial lighting time. Similarly, if one is using wax candles, care should be taken that they should be long enough to burn for at least half an hour after the appropriate candle-lighting time which is when stars appear in the sky. There are some multi-colored candles on the market made especially for small Menorahs which do not last for half an hour; one should abstain from using such candles. On Friday afternoon when Chanukah candles are lit earlier than usual, more oil should be added, as will be explained, G-d-willing, in a following Halacha.
Long Candles
According to the letter of the law, there is no reason to fill the glasses with more oil than is needed to light for a half-hour, for this was the edict of the Sages. Nevertheless, Hagaon Harav Yitzchak Ze’ev Ha’Levi Soloveichik zt”l, the revered Brisker Rav, ruled that since most people light on their windowsills today and there are still people walking and driving on the street until the late hours of the night, there is an extra special Mitzvah to have the Chanukah candles light for longer than just a half-hour. Maran zt”l quotes his opinion and seems to agree. This likewise seems to have been the opinion of Rabbeinu Chaim Palagi in his Ruach Chaim (672:2).
The above applies to one lighting Chanukah candles with oil. However, those lighting with wax candles should preferably use longer candles as this serves to beautify the Mitzvah, similar to using a beautiful Menorah.
The Mitzvah is Performed by Lighting
Our Sages taught us in the Gemara in Tractate Shabbat (23a) that the mitzvah of the Chanukah candles is performed through the lighting of the candles and if the candles are extinguished, one is not obligated to rekindle them. This means that the main Mitzvah is through lighting Chanukah candles which will innately have the ability to burn for half an hour. Therefore, if the candles were extinguished due to a non-existent cause at the time the candles were lit, for instance, if the door or window were opened suddenly and a gust of wind blew out the flames, one is exempt from rekindling the flames. Even so, it is an extra special Mitzvah to relight any candle (without a blessing) that has been extinguished if it is still within half an hour of being lit.
However, if the candle was extinguished before the halachic timespan of half an hour due to an intrinsic reason, for instance, because it was lit in a windy place or it was not filled with enough oil, one is obligated to relight the candle, albeit without a blessing.
Benefitting from the Candles
One may not derive personal benefit from the Chanukah candles. Thus, one may not use the light of the candles to aid in counting money or reading a book. After the candles have been lit for half an hour, however, one may use the light for whatever one pleases. Nowadays when electricity is common, we do not usually derive any benefit from the Chanukah candles in any event.