There’s many ways to improve light conditions, ranging from the Light cantrip to Devil’s Sight, but apart from magical darkness and actual blindness, does holding a torch or even having Darkvision actually matter in-game?
not as far as i know. a quick way would be to let the party run around in total darkness while being in the dungeon. this at least somewhat forces the player to equip torches or similar meanings of light to see the environment.
in the past i dabbled around with torches granting an area of effect to “cure” a special form of blindness, which was automatically granted when in total darkness. it quickly grew out of hand, giving all the different light sources, racial feats, special cases, needed triggers and so on and so forth. it’s too complex for the little immersion of gameplay it delivers.
It’s not like there’s any such thing as total darkness from what I’ve experienced, outside of magical darkness. There’s always that little bit of light that lets the player see.
you can plunge an area into pitch black, revealing nothing. plus you can design object interactions which check if the interacting character, or other characters near him, carries a light or has darkvision. if not, he can’t read or suffers a negative modifier.