Geometrical optics and ray tracing

Refraction and reflection at a boundary

• The Snell-Descartes law or law of refraction stipulates that

$ n_i sin\theta_i = n_t sin\theta_t $

with $ \theta $ the angle measured from the normal of the boundary, $ n $ the refractive index (which is unitless) of the medium, the subscripts $ i $ and $ t $ referring to the incident and transmitted light, respectively.