Realglow PL cobble is a synthetic aggregate, based on Realglow pigment and plastic. When exposed to light sources, the photoluminescent pigment within Realglow PL cobble becomes chemically excited and will afterglow (i.e. glow in the dark), initially very strongly, then reducing slowly overnight. The glow is best seen in a dark area, where ambient light sources such as streetlights and moonlight are absent.Realglow PL cobble is specially formulated from non-shrinking, extremely hard polyester for use in Concrete, Pavers and Terrazzo products as an exposed aggregate.