Reflectivity

Reflectivity is a term in radiometry. It is the ratio between the exitance from the front side of a surface and the incident irradiance on the front side.

$r_{\lambda }={\frac {M_{front,\lambda }}{E_{front,\lambda }}}$

Note that reflectivity is a unitless quantity in the range [0,1], and can also be expressed as a percentage in the range [0%,100%]. A completely transparent surface has a reflectivity of 0%, while a perfect mirror has a reflectivity of 100%. Reflectivity normally varies as a function of wavelength.

Reflectivity does not capture the angular dependence of the reflected energy; that is characterized by a BRDF.