The speed of light in a vacuum does not change. The speed of light in a non-vacuum medium can be different than the speed of light in a vacuum, however. And lig

The speed of light in a vacuum does not change. The speed of light in a non-vacuum medium can be different than the speed of light in a vacuum, however. And light passing from one medium to another changes speed (and is refracted). See https://en.wikipedia.org/wiki/Refractive_index https://en.wikipedia.org/wiki/Refractive_index