What is the source for lighting a candle on the anniversary of someone's death (yartzeit candle)? What are the sources for lighting such a candle on other days such as Yom Kippur, Yom Tov etc?
The reason for the yahrtzeit candle comes from the metaphor in
נֵ֣ר יְ֭הוָה נִשְׁמַ֣ת אָדָ֑ם חֹ֝פֵ֗שׂ כָּל־חַדְרֵי־בָֽטֶן׃
The spirit of man is the lamp of the LORD, Searching all the inward parts.