reflectivityreflectance
Reflectivity and reflectance refer to the fraction of incident electromagnetic energy that a surface or material reflects. They are dimensionless quantities, usually expressed as a ratio between 0 and 1 or as a percentage. In many contexts the terms are used interchangeably, but subtle distinctions exist: reflectivity often denotes an intrinsic property of the material at a given wavelength and polarization, while reflectance emphasizes the observed, geometry- and wavelength-dependent quantity.
Spectral, directional, and angular aspects are important. Spectral reflectance R(λ) describes how much light is reflected
The angular dependence of reflectance is governed in simple cases by the Fresnel equations for smooth interfaces.
Measurement of reflectance is performed with instruments such as spectrophotometers and integrating spheres to obtain spectral
See also: albedo, BRDF, Fresnel equations, spectral reflectance.