Bilipala 50 Pcs Blue Glow in the Dark Stones for Garden, Walkways, Yard, Outdoor Material: safe and environmental protection polystyrene resin. Warning: Do not use in the fish tank, can't shine in the fish tank. After being exposed to daylight, these pebbles glow in the dark. Glow lasts approximately two to three hours after full sun exposure. 50 pieces set of man-made pebbles. Products are mainly used for garden, walkways, yard, outdoor etc. Making your garden or yard looks different from your neighbors' at night.