Labyrinth Designer Post Cap Light for 4x4 Posts Inside Dimensions measure 3-5/8 x 3-5/8 inch. Fits 4x4 posts and is great for decks, fences, railings, porches Inside dimensions of 3-5/8" x 3-5/8" Loaded with a 1-watt LED bulb that runs on solar energy collected by its integrated solar panel Illuminates its immediate surroundings without consuming electricity 6-8 hours run time under a full charge