According to this thread celestia should break most DR (unless the mob has light immunity/resistance)
I pulled one on my paladin a few days ago and thought I'd give it a try.
So far it is not breaking any DR except good (which any weapon would since I have the paladin capstone)
I tried on various demons in the demonweb quests. Anything that needs cold iron I was getting yellow numbers on. Same for zombies in house of death undone (I think the zombie necromancer have light resistance but the regular ones shouldn't)
So does anyone know if this was changed from when the tests above were done or is the Paladin Capstone over writing the light damage and just treating it as "good" damage? (This seems likely to me as the combat log just says I am doing good damage)