By Zencalcy Editorial TeamLast reviewed About us
At one particular angle of incidence, light reflected from a dielectric surface is completely polarised parallel to the surface. That angle is named after David Brewster, and it is why polarising sunglasses cut glare from water and glass.
Angle at which reflected light is fully polarised.
tan θ_B = n₂ / n₁
θ_B is the Brewster angle, n₁ the incident medium and n₂ the reflecting medium. At this angle the reflected and refracted rays differ by 90°.
| Symbol | Meaning |
|---|---|
| θ_B | Brewster or polarising angle, from the normal. |
| n₁ | Refractive index of the incident medium. |
| n₂ | Refractive index of the reflecting medium. |
tan θ_B = 1.5, so θ_B = 56.31°. At this angle the reflected beam is polarised, and the refracted ray travels at 33.69° to the normal.
Continue with the Camera Exposure Calculator, Coherence Length Calculator, or the Critical Angle Calculator — or browse more optics and light tools and all physics calculators.
The component parallel to the plane of incidence vanishes, so the reflection is fully s-polarised. The transmitted light is only partially polarised.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Free calculator · No signup
Content updated: September 2026