4x4 Windsor LED Solar Fence Post Cap, 3-1/2" or 4" Post High-Quality PVC Solar Post Cap Lights up automatically and has an auto-off switch Stays lit for up to 10 hours 3 x brighter than standard LEDs Fits an actual 4" x 4" or 3.5" x 3.5" post (3.5" x 3.5" adapter included)