If you press the button, the light shines everywhere on the wall, except on the spot where you stand. You will see the shadow of yourself on a luminous wall.
This is because this wall absorbs light. When it gets dark again, it continues to emit light for a while. Except on the spot where there was no light, your shadow. Use a light pen to add a moustache, wings, crown, etc. to your shadow.
We also call this wall phosphorescent. Please note that this is not the same as fluorescent. You will notice the difference when you turn off the light. Fluorescent material stops emitting light immediately, think of a fluorescent jacket. Phosphorescent material, on the other hand, continues to emit light for several seconds to minutes.
Phosphorescence in glow-in-the-dark stars
Do you have luminous stars in your bedroom? They are also phosphorescent. During the day they absorb light, and when it gets dark, they continue to give off light for a while.