The glow in the dark pebbles can be used both indoors and outdoors. The pebbles do not glow until after being exposed to the sun during the daylight hours. Once they are exposed to the sunlight, they glow beautifully at night. There is no electricity needed in order to use these pebbles. They will glow for approximately two to three hours after they have been exposed to the sunlight all day. The glow pebbles are made from high-quality resin materials that are non-toxic, non-radio active, premium-quality 100% natural and they can be used to add beauty to the indoor or outdoor environment. You can use them when you want to add some decoration to your pathway, driveway, potted plants, flower beds or aquarium. They are safe to use indoors also but you have to make sure that they have been exposed to enough sunlight so they will glow when the lights are turned off. They come with 200 pieces in the colors of blue and green. For larger projects, you will need to purchase multiple packages of these rocks. This is a great product that I would definitely recommend.