You need Desura to install White Night (view standalone downloads)

Desura is installedLet's play! Install DesuraFor Windows(other versions)

Please Note: White Night installs in a complicated manner and may need to move or overwrite files in the Amnesia: The Dark Descent folder to work. While Desura attempts to manage this, it is possible that this mod may affect your game. We recommend you have a backup as Desura assumes no responsibility or liability for any issues that may arise by installing this mod, as stated in the terms of use.