These pebbles are made of plastic polystyrene and are coated with phosphorescent pigment. This pigment absorbs light and 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 your rose bushes, a bed of pansies, or a fence. Drop a handful into a bird bath. Creates a peaceful and 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 and path as well!