Perman 100 Pcs Glow In The Dark Stones Pebbles Rocks for Pet Fish Tank Aquarium Garden Material: Plastic. Quantity: 100. The size of 1 pc Pebble:1.7cm x 2.4cm/0.67'' x 0.94''(approx) Glow lasts approximately two to three hours after full sun exposure Line a walkway, edge a flower bed or decor garden, fish tank with these unique pebbles. After being exposed to strong daylight with 3 hours, these pebbles can be lighted within 1-2 hours in the dark.