Reflectance for unpolarised incident light
The Fresnel equations (or Fresnel conditions) describe the behaviour of light when moving between media of differing refractive indices. The reflection of light that the equations predict is known as Fresnel reflection.
When light moves from a medium of a given refractive index n1 into a second medium with refractive index n2, both reflection and refraction of the light may occur. The Fresnel equations describe what fraction of the light is reflected and what fraction is refracted (i.e., transmitted). They also describe the phase shift of the reflected light. The equations assume the interface between the media is flat and that the media are homogeneous. The incident light is assumed to be a plane wave, and effects of edges are neglected.
The light is said to be s-polarized when the incident light is polarized with its electric field perpendicular to the plane containing the incident, reflected, and refracted rays.
The light is said to be s-polarized, when the incident light is polarized with its electric field parallel to the plane containing the incident, reflected, and refracted rays.
The fraction of the incident power that is reflected from the interface is given by the reflectance or reflectivity R.
If the incident light is unpolarised (containing an equal mix of s- and p-polarisations), the reflectance is the average of Rs and Rp.
|R||Reflectance for unpolarised incident light (dimensionless)|
|Rs||The reflectance for s-polarized light (dimensionless)|
|Rp||The reflectance for p-polarized light (dimensionless)|