For Shabos, there is a custom to light 2 candles: one for shamor and one for zachor.
Shulchan aruch harav 263.1:
…אחד כנגד זכור ואחד כנגד שמור…
I understand that on yomtov they (the people that light on shabos) also light 2 candles.
Why?
Source?