Most clocks don't actually *glow* in the dark. They use a process called phosphorescence. Here's how it works:

* Luminescent paint: The numbers and hands of these clocks are coated with a special paint that contains phosphorescent materials.

* Absorbing light: During the day, the paint absorbs light energy (usually from sunlight or artificial light).

* Releasing light: When the light source is removed, the paint slowly releases the absorbed energy as light, making the clock appear to glow.

This glow isn't constant, but rather gradually fades over time as the stored energy is used up. This is why clocks that glow in the dark need to be "charged" with light regularly.

So, the clocks don't actually generate their own light. They are storing and releasing light energy they've absorbed.