The Brewster angle is the angle at which no reflection occurs in the medium of origin. It occurs when the incident angle $\theta_{B}$ is such that the reflection coefficient $\Gamma_{ \|}$ is equal to zero.The Brewster angle is given by the value of $\theta_{B}$ which satisfies

For the case when the first medium is free space and the second medium has a relative permittivity $\varepsilon_{r},$The above equation can be expressed as

Note that the Brewster angle occurs only for vertical (i.e. parallel) polarization.