Tangpan Man-made Glow in the Dark Pebbles Stone for Garden Walkway Pack of 100 (Mix Light) Line a walkway, edge a flower bed or fill a planter with these unique acrylic pebbles After being exposed to daylight, these pebbles glow (sky blue) in the dark Glow lasts approximately two to three hours after full sun exposure Pebbles are about the size of cooked lima beans