Darker is an option in the mobile version of Granny that was added in Version 1.0.5. To toggle it, find the box labeled Darker on the Main Menu, and tap on it.
On the PC Port of the game, you can't disable Darker because it is enabled by default on all modes. However, it looks completely different than it looks on the mobile version. For more information, read below.
Gameplay effects[]
Darker limits the player's field of view (with a black fog representing darkness), implying that the player has a limited view of what's ahead of them.
On the PC Port, Darker makes the house pitch black rather than shrouding it in fog. This is because a new item exclusive to the PC Port has been added: the Flashlight. Although the Flashlight makes it easier to see at a distance compared to the Darker on mobile, it casts shadows, making it difficult to see when hiding inside certain things.