Photo-luminescent, also know as "glow in the dark" materials incorporate inorganic phosphors into a carrier or substrate. In the case of our boat dock bumpers they are added into a thermoplastic material that is then co-extruded onto the surface of the bumper. These photo luminescent phosphors absorb light in the visible and ultraviolet wavelengths and release visible light in what is often termed as "afterglow". GaMra's boat dock bumpers will glow intently at sunset and then begin to lose their glow over time. Our testing has indicated a bumper is visible from 15 feet away after 10 hours.