Brewster angle and the Fresnel reflectance

What you are seeing: light incident on a planar dielectric interface from medium of index $n_1$ onto medium of index $n_2$. The reflectance for $s$-polarized light (electric field perpendicular to the plane of incidence) and $p$-polarized light (electric field in the plane) follow the Fresnel formulas. The right panel shows $R_s(\theta_i)$ and $R_p(\theta_i)$ over the full range of incidence angles. The animated ray sketch on the left shows incoming, reflected, and transmitted beams.

At Brewster's angle $\theta_B = \arctan(n_2 / n_1)$ the $p$-reflectance drops exactly to zero: light at this angle is reflected purely $s$-polarized. Polarizing sunglasses exploit this by filtering out $s$-polarized glare from horizontal surfaces. If $n_1 \gt n_2$, beyond the critical angle the wave undergoes total internal reflection and both $R_s$ and $R_p$ equal 1.