4x4 Solar deck lights (also called solar post caps) fits wood posts measuring 3-1/2" x 3-1/2" and are very easy to install. Choose from a wide selection of decorative solar powered post caps in luxurious copper, classic white, designer glass and more, to add the perfect finishing touch to your deck, fence, gate, sign, mail or dock posts. Just make sure they will get plenty of direct sunlight for easy dusk to dawn lighting.