Does the speed of light actually slow down during refraction, or does it just "take longer?"?

Light travels at a different speed in glass or water than it does in air or a vacuum. Speed of light in air is pretty much the same as a vacuum, but glass and water are significantly different.

When we say speed of light, we mean speed of light in a vacuum, and its constant for all light, of any color, energy level, etc, is why we say speed of light is constant.

But it isn't constant through all media...

It just takes longer to go through. Good question. There is a lot of confusion in the ranks.

The refraction index k = C/c, where c < C which is light speed in a vacuum means that light advances through that medium, whatever it is, at c speed. That is, something like a pin ball in a pin ball machine, photons, still going at C in between the atoms and molecules of the material, smack into those atoms and molecules and get either absorbed or rebounded by them. But in any case, their directions change like those balls when they hit a pin in the pin ball machine.

So the distances D = SUM(Ct) = C SUM(t) = CT, where t is the time between each bounce, traveled by those photons are longer when going through a medium other than a vacuum because the photons are not going straight. They are bouncing around, which means they take SUM(t) = T time to go S < D distance through the medium.

If we measured the time to go the distance S in a vacuum, that would be t = S/C. Then the speed of advance through the medium is c = S/T < S/t = C and we see that c < C. And we can make this into an equality by k = C/c, the refraction index.

To put it another way... no, the photons do not slow down in any medium. They simply bounce around and take longer to advance some distance S than they would have in a vacuum where they can go straight.

In a microscopic model, photons are absorbed and emitted by particles in the medium. Between each emission and absorption the photon travels at the speed it would in vacuum.

The idea that the medium can be treated as a just having a different permittivity and permeability (and thus a different index of refraction and wave speed) is an effective theory.

I slowed down as quickly as at a yellow mild and have been given hit from at the back of because of the fact the guy assumed i might save going. in view that then I velocity up and beat the mild fairly if a motor vehicle is at the back of me.