Since any polarization state can be resolved into a combination of two orthogonal linear polarizations, this is sufficient for any problem. There are two sets of Fresnel coefficients for two different linear polarization components of the incident wave. Main article: Plane of incidence The plane of incidence is defined by the incoming radiation's propagation vector and the normal vector of the surface. The incident light is assumed to be a plane wave, which is sufficient to solve any problem since any incident light field can be decomposed into plane waves and polarizations. The equations assume the interface between the media is flat and that the media are homogeneous and isotropic.

(The magnetic fields can also be related using similar coefficients.) These ratios are generally complex, describing not only the relative amplitudes but also the phase shifts at the interface. The Fresnel equations give the ratio of the reflected wave's electric field to the incident wave's electric field, and the ratio of the transmitted wave's electric field to the incident wave's electric field, for each of two components of polarization. When light strikes the interface between a medium with refractive index n 1 and a second medium with refractive index n 2, both reflection and refraction of the light may occur. For the first time, polarization could be understood quantitatively, as Fresnel's equations correctly predicted the differing behaviour of waves of the s and p polarizations incident upon a material interface. They were deduced by French engineer and physicist Augustin-Jean Fresnel ( / f r eɪ ˈ n ɛ l/) who was the first to understand that light is a transverse wave, when no one realized that the waves were electric and magnetic fields. The Fresnel equations (or Fresnel coefficients) describe the reflection and transmission of light (or electromagnetic radiation in general) when incident on an interface between different optical media. Polarized sunglasses block the s polarization, greatly reducing glare from horizontal surfaces. At near-grazing incidence, media interfaces appear mirror-like especially due to reflection of the s polarization, despite being poor reflectors at normal incidence.

Malus equation light intensity