Light normally vibrates in many different directions as it travels through empty space. When this normal light hits a glass window, some light reflects and some passes through. The Brewster angle represents a special geometric relationship between these reflected and passing beams.
At this magical angle, the reflected ray and the refracted ray sit exactly 90 degrees apart. This perfect right angle prevents one specific polarization of light from reflecting at all. The light vibrating parallel to the plane of incidence passes completely through the clear material.
Only the light vibrating perpendicular to the plane bounces back toward your eyes. This missing parallel light makes the final reflected beam exactly 100 percent polarized. The specific value of this angle depends entirely on the materials involved in the boundary.
You must know the refractive index of both the starting material and the target material. Students often think this angle only applies to visible light hitting glass or water. However, this polarization effect happens with all types of electromagnetic waves hitting non-metallic surfaces.
Engineers use this exact principle to design special camera filters that block annoying glare. Chemists also use this angle to study extremely thin chemical films on liquid surfaces.