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What light may one use to check for Chametz?
A single wicked candle: When checking at night the search may only be done using the light of a candle. One may not use the light of a torch to search the Chametz, but rather one is to search with the light of a small single [one wicked] candle. If one transgressed and checked using the light of a torch, he does not fulfill his obligation and must repeat and check using the light of a single wick candle, without a blessing.
The definition of a torch: An oil candle which has two wicks is considered a torch, and thus if one transgressed and used it to check, he must recheck his house. Similarly, if one took two bees wax candles and placed them near each other and checked with them, the Bedika is not valid. Even if one went ahead and braided the two candles into one, or melted them until they became one candle, nevertheless since it contains two wicks it is considered a torch.
The wax: Lechatchilah, a beeswax candle [or paraffin candle] should be used. [Nevertheless, based on Kabala one is to use specifically a beeswax candle, and so is the Chabad custom.] If this is not available, then one may use a candle made of any kosher wax. If this is also not available then [non-kosher fat] Cheilav should be used. If this too is not available then oil should be used. An oil candle should not be used in other circumstances. In all cases, if one did the search using one of the above candles, even if a better candle was available, he has fulfilled his obligation and does not need to repeat the search using a bee’s wax candle.
Using wood: One may not use a lit piece of wood as a candle. This applies even if one has a single piece of strong wood which lights well, such as cane, nevertheless it should not initially be used if one has a bees wax candle available.
One is not allowed to check with a torch. If one did so, he must repeat the search without a blessing. Lechatchilah a beeswax candle should be used.
May one use a flash light or a florescent light in the room to do the Bedika?
It is permitted to use a flash light or other form of electric light for the Bedika. Nevertheless, the custom is to use specifically a candle for the Bedika. However, in a situation that the electricity is needed to help one do the Bedika, then one should not refrain from using it together with the candle. Similarly, those areas which one cannot check properly with a flame due to fear of causing fire, then even Lechatchilah a flashlight should be used. If one does not have a flame available, then he may even Lechatchilah use a flashlight and say a blessing over it.
The Bedika kit:
The custom is to perform the Bedika using a bird’s feather, wooden spoon and bees wax candle. The Chametz that is found is placed into a paper bag. At the end of the Bedika one places the feather, leftovers of the candles, if applicable, and the wooden spoon together in the paper bag. The feather and leftover candle is to be placed inside the spoon, and then wrapped with the paper bag. The handle of the spoon is to remain unwrapped, and extend above the paper bag. One ties the top of the bag around the spoon using a string.
 Admur 433:1-6
 Admur 433:1
Moon light: Using the moon light does not suffice, as the light of a candle is good for checking and searching in hidden places, holes and cracks, [as opposed to moonlight]. [Admur ibid]
 Admur 433:8-9
The reason: The reason for this is because the light of a torch cannot enter into holes and cracks. Furthermore, one is afraid of it burning down the house and will have his mind/heart troubled by this fear during the search which will prevent him from searching properly. [Admur 433:8]
 Admur 433:9
Background and other opinions: If one transgressed and checked using the light of a torch, then he has not fulfilled his obligation and must repeat and check using the light of a single candle. However there is an opinion [Taz 433:3] who rules that one does not need to repeat the search. Practically [we rule like the former opinion that the search must be repeated, but] one should suspect for the latter opinion and not repeat the blessing when he rechecks the house. [Admur ibid]
 Admur 433:10
 Admur 433:8
 Chemically made wax candles may be used even Lechatchilah, being that the entire restriction against other waxes is due to worry that a non-kosher substance will drip on the vessels, which is not applicable by chemically made candles.
 The deficiency of other material candles: Lechatchilah one should be careful to only use a bees wax candle to search, and not candles made of non-kosher fat, as [while checking with it] one [will] fear that it will drip onto ones kosher food utensils [and will thus not be able to check properly]. As well, candles made of Kosher fat should also not be used being that one fears of it dripping on his dairy utensils. An oil lamp should also not be used because one fears of it dripping onto one’s clothing and staining them, as well as being that one cannot enter well such a lamp into holes and cracks. [Admur ibid]
 Likkutei Taamim Uminhagim of Rebbe on Haggadah; Piskeiy Teshuvah 433:2
 The reason: By pressing times, such as when one does not have any bees wax candles to use, it is considered like bedieved, and he may even lechatchilah use other candles to check. Nevertheless, if one is able to check with kosher fat candles, he should do so rather then check with a non-kosher candle, as when checking with kosher fat he only fears from dripping on milky vessels as opposed to meat vessels while when checking with non-kosher candles one fears from it dripping on any food vessel. [Admur ibid]
 The reason: If one does not have kosher candles, then non-kosher wax candles should be used rather than oil, being that an oil candle cannot be entered well into holes and cracks, as can wax candles. [Admur ibid]
 Admur ibid; Kuntrus Acharon 433:2
Other opinions: Some Poskim rule that an oil lamp has the same status as a torch, and if it was used then one must recheck. [M”A 433:15, brought in Kuntrus Acharon 433:2] However, all the other Acharonim argue on this, and so seems logical being that this is not mentioned in the Talmud, as well as that by a Rabbinical dispute we always are lenient, and especially here where the majority of opinions are lenient, not to mention that according to the Taz one never has to recheck even when a torch was used. [Kuntrus Acharon 433:2]
 Admur 433:11
 The reason: Being that wood does not light well when it is a single piece, and if there are two pieces of wood, even if they are very thin, then it’s considered a torch. [Admur ibid]
 The reason: As since it gives off a bad smell as well as that sparks fly off from it when it is lit, there is suspicion that because of this one will not be able to check well. [Admur ibid]
 See Sheivet Halevy 1:136; Piskeiy Teshuvos 431:2
 There is no true reason to differentiate between light of a candle and electricity, as the main thing is to search for the Chametz properly, which both a candle and electricity accomplish. Nevertheless, the Jewish people remain loyal to the original tradition of using a candle rather than electricity. The Chabad custom is to use a beeswax candle.
 Sheivet Halevy ibid; as the main thing is to check properly. [ibid]
 Piskeiy Teshuvos ibid
 Likkutei Taamim Uminhagim of Rebbe on Haggadah