A. The Mitzvah to light candles:
On every Shabbos and Holiday there is a command to honor the day through eating a festive meal. Now, being that we cannot honor Yom Kippur through eating, due to the commanded fast, therefore, the Torah commanded us [in its stead] to honor it through wearing clean clothing and lighting candles. Thus, one must honor Yom Kippur through lighting candles, and it is a Mitzvah to do so, just as is done on every other Erev Shabbos and Yom Tov.
Married couples: Despite the above obligation, some communities are accustomed to prohibit married couples from lighting candles in their home on Erev Yom Kippur, in order to prevent them from seeing each other, which can possibly lead to marital relations. In other communities, however, couples light candles in their home [and room] in honor of Yom Kippur. Those communities who light candles are to recite a blessing, as will be explained. [Practically, the custom today amongst all communities is for even couples to light candles with a blessing.]
When Yom Kippur falls on Shabbos: In years that Yom Kippur falls on Shabbos, according to all one must light Shabbos candles [and thus also leave a light on in the couple’s bedroom, as explained next].
The blessing: After lighting the candles for Yom Kippur, one says the blessing of “Asher Kidishanu Bemitzvosav Vetizvanu L’hadlik Neir Shel Yom Hakippurim.” If Yom Kippur coincides with Shabbos, one says “L’hadlik Neir Shel Shabbos Veshel Yom Hakippurim.” One then recites Shehechiyanu.
If one said accidently said “Shel Yom Tov” or “Shel Shabbos” does she fulfill the obligation?
Some Poskim write that if one said, “Shel Yom Tov” he/she fulfills their obligation. If, however, one said “Shel Shabbos” then he/she does not fulfill their obligation. According to all, if one remembers within Kdei Dibbur, he/she is to correct himself/herself.
If Yom Kippur fell on Shabbos and one only said the blessing of Yom Kippur, what is he/she to do?
Some Poskim write that he/she is not required to repeat the blessing of Shabbos. The same applies vice versa.
If a man is lighting candles, is he to say Shehechiyanu by candle lighting?
When a man lights candles, he does not recite the blessing of Shehechiyanu by candle lighting, rather, it is said in Shul together with the congregation. If he did say it by candle lighting, then he may not repeat it later on.
If a man is lighting candles, does he first light the candles and then say the blessing or vice versa?
Some Poskim rule men are to follow the same order as women, and are hence to first light the candles and then say the blessing. Other Poskim however rule that men are to always first say the blessing and then light the candles. [See footnote for opinion of Admur]
Must a woman remove her leather shoes before lighting candles?
B. Leaving a light on in the bed room of married couples:
If a couple is leaving a light on in their house [on the night of Yom Kippur], then they are required to also leave a light on in their bedroom. This applies both in areas that are accustomed to light Yom Kippur candles at home, and in communities that are not accustomed to light Yom Kippur candles. [Thus, being that the custom today in all communities is to leave lights on in the home, therefore, a married couple is obligated to leave a light on at night in their bedroom. Seemingly, this candle is to remain lit throughout the night. Due to safety reasons, one should not light an actual candle, but rather simply turn on a lamp or night light that will remain lit throughout the night.]
On Erev Yom Kippur, a married couple must leave a light on in their bedroom.
If one’s wife is a Niddah must they light a candle in the room?
No. There is no need for a candle to be lit in their room. [However, some Poskim write that in areas accustomed to light Yom Kippur candles, which is all areas today, then they are likewise to leave a light on in the marital bedroom, even if the wife is in a state of Niddah.]
How long must the light remain on for in the bedroom?
The candle or lamp must remain lit until the morning.
Is leaving a night light on in the bedroom a valid form of light?
C. Lighting above the ill and in alleyways:
On Erev Yom Kippur, it is customary in all communities to light candles near sick people and in dark alleyways.
D. Lighting candles in Shul:
On Erev Yom Kippur, candles are lit in Shul. In the past, it was customary for every male, young and old, to light a candle in Shul. However, today the custom is only for married men to light a candle in Shul. [This candle is customarily called a Gezunt Licht.]
Having a gentile extinguish the candles: Being that many candles are lit in Shul, the custom became to hire a gentile to guard the Shul to prevent the spread of fire. However, from this descended a custom to allow asking the guard to extinguish or light the candles. In truth, there exists no Halachic permission for asking the gentile to do so. Such a person is to be protested, especially on the Day of Judgment.
If the candle extinguishes: If the candle that one lit extinguished on Yom Kippur, it is a bad omen. To rectify this, he should relight the candle after Yom Kippur and let it burn out on its own. So too, he should accept upon himself that every year thereafter in which the candle remains lit after Yom Kippur, he is not to extinguish it but rather let it go out on its own. [To avoid this issue, some suggest placing the candle in Shul together with all the other candles, and hence avoid knowing which candles belongs to whom.]
E. Lighting a Yartzeit candle:
The custom is to light a [24-hour] candle for a deceased parent on Erev Yom Kippur.
Leaving a 24-hour candle on in the house for Havdala:
One is to light a 24-hour candle in his home to be used for Havdala on Motzei Yom Kippur. See Chapter 5 Halacha 6!
 Admur 610/1-3
 Admur 610/8 in parentheses
 Admur 610/1; M”A 610/1; Rosh 8/9; Mordechai 725
Other opinions: From some Poskim it is implied that there is no Mitzvah to light candles on Erev Yom Kippur. [See Rambam laws of Yom Kippur chapter 3/10]
 Admur 610/1; Michaber 610/1; Mishneh Pesachim 53b
 The reason: They do not suspect that seeing each other will lead to relations, being that it is prohibited to have relations in front of light. [Admur ibid] One can suggest that this opinion does not argue on the fact that leaving the light off is a greater distance from relations than to leave it on. Rather they claim that being there is a mitzvah to light candles, one may not nullify the mitzvah simply in order to make a greater distance, and the distance of having a light on suffices. Furthermore, according to all opinions, it seems that if theoretically having the lights on would not distance relations, then we would forbid lighting candles for Yom Kippur, despite the mitzvah involved. To note: From the Rambam laws of Yom Kippur chapter 3/10 implies that there is no mitzvah at all to light candles for Yom Kippur and the only reason why some people light is to prevent relations. According to this, it ends up that the distance of lighting candles is greater than the distance of not lighting, unlike the implication of the wording above.
If the actual prohibition of having relations on Yom Kippur is not enough on its own to prevent it from happening then why would the lighter prohibition of not having relations in front of light prevent them? Perhaps since a person is accustomed to never have relations in front of light therefore he is more accustomed to hold himself back if there is light, despite it being a less severe prohibition. While the prohibition of Yom Kippur alone, although more severe, since one’s inclination is not used to controlling himself in such a situation, therefore there is more of a chance for him to stumble.
 Piskeiy Teshuvos 610/1
 Admur 610/3
 Admur 610/1; Siddur
 The reason: As Yom Kippur contains a Mitzvah to light candles just as Shabbos and Yom Tov. [Admur ibid]
 Mahram Brisk 2/44; Piskeiy Teshuvos 610/1
 Mahram Brisk 2/44; Piskeiy Teshuvos 610/1
 Luach Kolel Chabad
Other opinions: Some write that on Erev Yom Kippur, even men should say Shehechiyanu by candle lighting as they will not be saying Kiddush that evening. [See Moadeiy Kodesh 3/167; Piskeiy Teshuvos 610 footnote 8]
 See Admur 263/8; Piskeiy Teshuvos 263 footnote 168
 Derech Hachaim 50/7; Ketzos Hashulchan 74 footnote 19; Customs in new Siddur Tehillas Hashem; Maharam Shick 119; Birchas Habayis 45/4
 Aruch Hashulchan 263/13; Toras Yekusiel 61; Ashel Avraham Butchach; Piskeiy Teshuvos 263/18
The reason: As men do not accept Shabbos right away upon lighting. [See 263/7]
 Some rule based on Admur [who does not differentiate between men and women] that men follow the same order as women and light before the blessing. [Ketzos Hashulchan 74 footnote 19; Customs in new Siddur Tehillas Hashem; To note the Nesiv Hachaim also did not argue on the ruling of Derech Hachaim ibid] Others however rule that according to [the M”A and] Admur [who states the above custom to first light in Lashon Nikeiva, in contrast to the wording of the Rama] men are to first say the blessing and then light. [Piskeiy Teshuvos ibid] Vetzaruch Iyun on the above Poskim who did not infer differently from Admur, as seems clear from his wording and as writes Piskeiy Teshuvos.
 SSH”K 44/14; Piskeiy Teshuvos 608/1
 Admur 610:2; Rama 610:1; Maharil Erev Yom Kippur p. 321; Mateh Efraim 610:2; Chayeh Adam 144:14; M”B 610:5; Nitei Gavriel 25:1; Shevach Hamoadim
Other opinions: The Magen Avraham 609/2 brings and justifies that the custom is to be lenient even in such a case, to not leave a light on in the bedroom, although he concludes to be stringent. Thus, Admur rules like the stringent conclusion of the Magen Avraham without making mention at all of a possibility for being lenient.
 The reason: As since one can see his wife due to the light that was left on, in the home, there is therefore suspicion that he may desire his wife and enter into the dark bedroom to perform marital relations. [If, however, one leaves a light on also in his bedroom, he will not come to sin.] [Admur ibid; Rama ibid; Maharil ibid] This means as follows: Even according to the custom that avoids lighting Yom Kippur candles, they agree that if they will regardless be seeing each other, then, in this situation, the best way to distance relations from occurring is to also leave a light on in their bedroom, being that its forbidden to have relations in the light. [Meaning, according to all we only say that not seeing each other is a greater form of distance from relations than leaving a light on, in a case that they will not see each other at all. However, if they will see each other anyways, then its best to leave the light on in the bedroom in order to at least have this form of distance from relations.]
 Admur ibid; M”B 610:4; Kaf Hachaim 610:5
 P”M 610 A”A 2; M”Z 1; M”B 610:5; Kaf Hachaim 610:6
 Shaar Hatziyon 610:4; Kaf Hachaim ibid
 Hisorerus Teshuvah 398; Nitei Gavriel 25:1
 Nitei Gavriel 25:1 footnote 1
 Admur 610/3; Michaber 610/3; Mishneh Pesachim 53b
 Admur 610/4
 This implies even a child below the age of 13.
 Admur ibid; Rama 610/4; Mordechai 723; Maharil p. 322; Mahariy Viyal 191
 Admur ibid; M”A 610/3
 Admur 610/7; M”A 610/4; Maharil ibid
 610/8; Rama 610/4
 Seemingly this refers to the candle which he lit in Shul.
 M”B 610/14 in name of Chayeh Adam
 Admur 610/5; Rama 610/4; Kol Bo 68
 M”B 624/13 in name of Derech Hachaim