Ghost (Fallout Supplement)
From D&D Wiki
When the sun goes down, or you are in a poorly lit area, you move like a Ghost with this feat.
Prerequisite: Level 4, 4 skill ranks in the Hide and Move Silently skills
Benefit: Gain a +2 bonus to Hide and Move Silently skill checks and three-quarters cover when hiding in darkness (when the sun goes down, in caves, ect.).