Has anyone taken into account on how obscurity would play into all this?
Because the Underdark is... well... dark. And obscurity is a serious penalty factor in there, which acts as an advantage for the enemy and a disadvantage for the party. It's basically treated as a hostile environment because of this.
So by having night-time, it would primarily boil down to obscurity battles just like the Underdark does now, which seriously limits certain races/classes without being prepared for it.
