The Search and Nullification of Chometz
2. [When searching for chometz on the night of the fourteenth] one should
use only a single-wick beeswax candle for the search (1). One should not
use a braided candle, because it is considered like a torch ("avukah")
(2). In a pressing situation, when there is no beeswax candle available,
one may use a tallow ("cheilev") candle (3).
(1) The sages of the Talmud enacted that a candle should be used for the
search, because daylight is insufficient for searching in holes and
crevices. Nowadays, a flashlight may be used, however, in order not to
deviate from the traditional custom, many begin the search with a candle
and then use the flashlight for places where the candle would be
inadequate or dangerous ("Halachos of Pesach" by Rav Shimon Eider VII D7).
(2) A torch is too large to be brought into holes and crevices.
Alternatively, the light produced by a multi-wick candle is not conducive
for this type of search. If one conducted the search using only a multi-
wick candle, the search is invalid and must be conducted again (See
Pesachim 8 and Mishna Berura 433:8 and 10).
(3) When other types of candles are available, one is not permitted to use
a tallow candle because people would be concerned that the fat would drip
on the dishes and render them non-kosher. Consequently, one would not
search properly in cabinets containing dishes (Mishna Berura 433:9)