These pebbles glow beautifully, and for a very long time. But the brightness and length will vary according to how they are used. I place them at the base of lamps to be used as night lights, once the lamp is turned off for the night. They are very bright to begin with, and will still be glowing hours later, albeit not as brightly...but that is the nature of glow in the dark items. They are not solar lights that maintain the same brightness until they lose their charge. For those expecting those results outside, it will not happen. There is too much lag time from the time the sun sets, to total darkness, and the pebbles will lose much of their glow by then. And unless you live hundreds of miles from other houses, and cities...it's never as dark outside as you are able to make it inside. There is usually light pollution as well as the brightness of moonlight. These are much better suited for indoor use to appreciate the full effect, where you are able to go from light to complete darkness instantly. Also, a single layer works the best. Anything more is a waste because the light can't reach beyond the top layer and those beneath will not be charged, so they won't glow. When used correctly, these are beautiful!
I read all the reviews and decided to just give it a shot, but they totally do not work for the purpose I bought them. I have a small backyard pond whose edges are lined with river rock and pebbles. I was having a party and got these to toss around the edges of the pond to add some glow. I was excited when they came, because when charged up and then put in a dark place, they glowed just fine. That's why I give them 2 stars - they actually *do* glow. However, when placed outside, they apparently lose whatever charge they have by the time the sun is completely gone, and they only have the barest, faintest, most miniscule hint of glowing (and I mean infinitesimal.) It's more like you just notice that there are solid white pebbles amongst the rest of the rocks rather than actually tracking that they might be glowing.
So, yeah, not effective at all for outside decoration. I left them there just because I didn't feel like picking them all up again, and I just let the little kids find them and put them in their pockets to take home so that they'll actually get some use.