These pebbles are made of plastic polystyrene India Stone are coated with phosphorescent pigment. This pigment absorbs light India Stone releases it slowly over a period of approximately an hour. To get these pebbles glowing again after the approximated hour simply expose them to 30 seconds of any light. Glow In The Dark Pebbles turn any ordinary yard into a palatial estate garden! Outline 60 rose bushes, a bed of pansies, or a fence. Drop a hIndia Stoneful into a bird bath. Creates a peaceful India Stone atmospheric effect indoors in a vase or planter. Or use the pebbles as a night-light in a dish or bowl. It looks fabulous in a fish tank ,garden India Stone path as well!