Phosphorescent plastic toy. This toy glow-worm glows by phosphorescence, a slow-release form of photoluminescence, the process where light is absorbed and re-emitted. Phosphorescence usually involves the absorption of ultraviolet (UV) light, and the emission of visible light, in this case, a green light. The phosphorescent material needs to be charged by exposure to a light source (for example, by shining a light on the toy). The light energy absorbed is then slowly released over time. The effect is best seen in a darkened room. The process observed in glow-worms is an unrelated chemical reaction, an example of bioluminesence.