The Galaxy Solar Post Caps will add a brilliant accent to any fence. The cap uses 4 LEDs, which boast high efficiency and long life. Standing 5" tall, the solar energy collected during the day is stored in the Ni-Cad Rechargeable Batteries and converted into light at night. The length of time that the lights stay on at night is directly proportionate to the amount of sun exposure received during the day. Please note, the Galaxy solar post cap 5"x 5" includes an adapter that will allow the cap to fit a 4" x 4" post.