The glow -in -the- dark works by absorbing  light from a nearby

source, similar to glow-in-the-dark plastic toys. Standard  florescent, actinic , or incandescent (ordinary light bulb) aquarium lights work great. Natural sun light works great too, but it really needs to be right next to the window so sunshine actually hit it! The closer they are to the light, or the brighter the light, the faster they will " charge up" and the longer they will glow!! What does not work though is the regular LED lights, the ones that are rows of dots. These give off a different kind of light that the glow glaze does not absorb.