Glowing Rocks - Grow in The Dark Pebbles, Resin DIY Stones for Fish Tank/Aquarium/Driveway/Walkway Décor - Luminous Rocks/Gravel (Green, 100 PCS)

You need them in DIRECT sun for they to charge the chemistry. Once charged, they will shine very brightly if you take them in a dark place... But for a short time. When left outside, by the time the sun is down and it's dark, they've exhausted their light. So pretty much not useful.They're about 1" in size, not huge. I put them in a flat glass plate.

I received my stones yesterday - ordered 200 pieces and only got 178 pieces so don't think it was as good value as it seemed. Was really disappointed in not receiving the promised amount.