"Friend of the Night (1 Rank)
Prerequisite: Sneak 30, Perception 6
You are a true friend of the night. Your eyes adapt quickly to low-light conditions indoors and when darkness falls across the post-nuclear wasteland."
This works great outdoors during the night time hours. However, when I'm inside a building that's dark (for example the basemant at REPCON), the ability only works in the basemant during the night time hours. Based on the wording of the perk, it should work 24 hours a day when in low-light conditions.