What does it mean that light "slows down" in glass?
Open with LBRYA link to the full video is at the bottom of the screen.
Or, for reference: https://youtu.be/KTzGBJPuJwM
That video unpacks the mechanism behind how light slows down in passing through a medium, and why the slow-down rate would depend on color.
Editing from long-form to short by Dawid Kołodziej
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https://www.youtube.com/watch?v=XIW-2ykgVPI