The Shulhan Aruch (Orah Haim 514:5) rules that although it is generally permissible to light a candle from an existing flame on Yom Tob, one may not light a "Ner Shel Batala" – a candle that serves no purpose. If a person does not need the candle for cooking, for light, or for a Misva, it may not be lit on Yom Tob, even from a preexisting flame.
In light of this Halacha, the question arises as to whether one is allowed to light a Yahrtzeit candle on Yom Tob in memory of a parent, other family member, or one of the Sadikim. Does this qualify as a candle lit for a purpose, such that it is permissible, or is it considered a "Ner Shel Batala" since it does not serve a practical function?
Hacham Bension Abba Shaul (Israel, 1923-1998) addresses this question in his work Or L’sion (vol. 3, p. 207; listen to audio recording for precise citation), where he writes that it is permissible to light a Yahrtzeit candle on Yom Tob. Since the candle is lit to give honor to the memory of a loved one or a distinguished Sadik, it serves a significant purpose and is thus not considered a "Ner Shel Batala." This is especially so, Hacham Bension adds, if the candle is lit in the synagogue, which gives honor to the synagogue and thus certainly serves a significant function.
This is also the ruling of the Be’ur Halacha (Rav Yisrael Meir Kagan of Radin, 1839-1933), in the aforementioned Siman (Dibur Ha’mat’hil "Ner Shel Batala"), and this is, indeed, the Halacha.
Summary: It is permissible to light a candle from a preexisting flame on Yom Tob, provided that the candle is needed for a purpose, such as cooking or light. A Yahrtzeit candle lit to honor the memory of a deceased person is considered as serving a meaningful purpose, and it is thus permissible to light such a candle on Yom Tob.
