Most people are pretty clear about the phosphorescent glow and how it works. It is explained in a simple way about how, if you have one of those many "glow in the dark " items, they will be activated by an exterior light source and the sustaining glow will last pretty much in direct proportion to the amount of light that gets absorbed. The light source can be direct sunlight, a regular light bulb, or most effectively by a UV blacklight.
Below, a meditation rock was painted with phosphorescent paint and showcased under regular light (and) a UV blacklight to show how it appears on both sides after being activated. You may notice that the glow factor won't last that long... but at least will last long enough that you should still be able to find it without a usual light source available.