Light changes direction slightly when passing from one substance to another?

This phenomenon is known as Refraction.

Explanation:

Light waves change speed when they pass across the boundary between two substances with a different density, such as air and glass. This causes them to change direction, an effect called refraction.

At the boundary between two transparent substances:

the light slows down going into a denser substance, and the ray bends towards the normal

the light speeds up going into a less dense substance, and the ray bends away from the normal

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