Michal has a T-shirt that glows in the dark he holds his T-shirt up to light source and then turns off the light his T-shirt continues to glow. Explain this phenomenon?

Answer: Residual fluorescence.

Explanation:

The T-shirt is first kept in the light source for 10 to 15 minutes or more and then when it is taken to a dark place it glows.

This phenomenon is known as residual fluorescence. The t-shirt contains phosphors. It is a visible light which is seen after it is energized.

When the T-shirt is under a light source it is basically in a charging mode and then after some time in the dark it glows due to the phosphors mixed in the fabric.

This is also in some of the toys, watches and other stuffs that glows in the dark.