Birdmark Afterglow is a perforated disc, containing all of the reflective and luminescent properties for migrating birds in both daytime and nighttime flight. The disc absorbs and emit purple ultraviolet light visible to the birds as violet but appears as white plastic to humans. You will see the product glow for 10-12 hours after sunset. The Birdmark alert passing birds of obstruction ahead on the marked wire. The product wiggles in the wind back and forth to flash at approaching birds during windy days.