A lighted post cap assembly includes a base member with a generally square shape, a floor, and a plurality of perimeter side walls. The base member is configured to receive an upper end of a post and the floor defines at least four alignment guides and at least four rectangular shaped through holes. Each alignment guide and each rectangular shaped through hole is disposed proximate a respective perimeter side wall. A plurality of light sources are contained within a housing, and each light source is configured to be received by a respective alignment guide at a respective rectangular shaped through hole and oriented downward to illuminate a perimeter of the post. A cover has perimeter side walls and a roof and is secured to the base member such that the plurality of light sources contained between the base member and the cover.