Light reflected 90° out of phase, not 180°

[damosuz]

Classically, we explain why light appears to move slower in glass by saying that the electrons in glass emit a light wave which is 90° out of phase with the light wave shaking them. However, the electrons would have to emit this wave not only in the incident direction, but in the opposite direction as well, which would be the reflected wave. This means the reflected wave is 90° out of phase with the incident wave, and not 180° as it is mentioned everywhere (often by making an analogy with string attached to a rigid wall). What am I missing here?

 

[blue_leaf77]

the electrons in glass emit a light wave which is 90° out of phase with the light wave shaking them

This is new to me. Can you mention the source?

 

[damosuz]

Here: https://en.wikipedia.org/wiki/Refractive_index#Microscopic_explanation

Feynman says same thing in his lectures.