What ifyou also have stunted magicka and no restore magicka potions?
But what if you are dead -.-
It could have places where light come from holes, illuminating small portions of it with sun/moon light. Also things that are 1 meter away from your character could still be seen, but not in full spectre of colors, only black/brown shadowy shapes.
And all bandits and marauder dungeons should have torches on some walls, and the bandits and marauders should be carrying a few torches with them as well.
Beast dungeon would surely not be populeted if there was pitch black 24/7, so holes in the "roof" of the′dungeon should be enough for any adventurer to navigate away from there, but they should not see things and enemies without torches/spells, unless the enemy is under a strem of light.