We've had several Zisc discs these past 3 years and couldn't be more impressed. Still have 2, but lost the glow-in-the-dark one a few weeks ago, down the Wenatchee River, at lunch-time. It holds its glow for 30 minutes at least, so we'll need to purchase another before Winter. All I do is hold it against my car's headlight for 30 seconds or so, and it's bright enough to see for hundreds of yards. Rocky loves the water all year long, so I was amazed how the disc glowed in the cold river after dozens of throws! It's even visible under a few inches of powder snow on a dark night.
The only drawback is that in broad daylight, when the disk lands in the water,it becomes almost transparent, virtually invisible. That's how we lost our last one. But we've still got our big blue one (for calm days) and our small orange one (for windy, gusty days-- easier to control) to keep us busy and happy during the long hot 'dog days' of summer.
Thanks for making such a great product!