The Gemara in Menachos (41b) says: “It was stated: Rav holds that one may not use one candle to light another, and Shmuel holds that one may. […] Abayei said: With regard to every law but these three (including the one quoted above) [Rabba] followed the opinion of Rav, but for these three he followed Shmuel.” Rashi and others point out that the Gemara refers to the candles lit on Chanukah. (See the poskim in Orach Chayim 674 regarding other obligatory lightings.)
Rabbeinu Gershom on the Gemara explains like Rashi, that the discussion here is about Chanukah candles, but adds an explanation of Rav’s position. He writes: “[According to Rav] one may not light one candle with another because one thereby diminishes the [object of] mitzvah.” At first glance this seems innocent enough. He simply intends to explain that Rav’s objection stems from a concern that using a mitzvah-purposed candle to light other candles – even other mitzvah candles – causes the former to be somehow diminished.
The Lamdan 