The best way to charge glow in the dark objects is with a 365nm or 405nm UV Flashlight (Not Black light). This kind of light can penetrate the strontium more deeply. UV light penetrates the strontium atoms emitting photons, resulting in a brighter glow. Charging with UV light takes around one minute (longer the better) and glow can last anywhere from 20min-6 hours depending on the color of glow powder. Some colors like red, purple, dark blue will glow for a shorter time due to the properties of those glow powders.