How does light accelerate back to its original speed after refraction from another medium e.g. glass or water

Question

The speed of light slows as it traverses through a different medium, but after slowing it finds a way to accelerate back to original speed as it exits that medium. How does it do that?

In: 93

Answer 1

I have no idea, but what goes through my mind right now is: Photons don’t have mass, therefore they don’t need any energy to accelerate since F = m*a.