Ah the good ol painful light farm. Three of my favorite pick for Nexus and Zeta (the last) phase are Tam-tara, Stone Vigil, and Aurum Vale. What I did:
  • Fish for light bonus period by unsyncing these three dungeons.
  • If I manage to catch one of them giving 'Blinding' light bonus, I turn up my music, and spam as much as I can until this bonus window is over.
  • If neither of these 3 gave light bonus, I just do Aurum Vale 2 more times to ensure my weapon is at least gaining 1 tier of progress to completion.

Why Aurum Vale? Like Iscah & Drip mentioned, it's actually shorter and possibly the fastest. Morbol seeds can be ignored as long as you keep moving forward. They will hatch but the seedlings won't aggro you if you're too far away. Big morbols are primary target because their death will open up the blocked passages. Otherwise nothing else is gating you beside boss encounter from keep moving on.

If I do get bonus window for Stone Vigil, I always make sure to save my burst buttons to ensure I can force the dragon to skip their untargetable phase. It is otherwise another fast dungeon with very little 'gates'.