is the change in direction of light that occurs when it passes through
materials with different refractive indices.
is well studied in physics, and is described by Snell’s law, which relates the
angle of incidence θi to the angle of refraction, θr as
ni and nr are the indices of refraction of
the respective media.
value of η = 0.66 corresponds to an
air / glass interfaceSource: The Sundial Primer