Editing Specular reflection (section)

== Reflectivity ==
''[[Reflectivity]]'' is the ratio of the power of the reflected wave to that of the incident wave. It is a function of the wavelength of radiation, and is related to the refractive index of the material as expressed by [[Fresnel's equations]].<ref>{{cite book | first=Eugene |last=Hecht |year=1987 |title=Optics |edition=2nd |url={{google books |plainurl=y |id=oiSrQgAACAAJ020111609X}} |publisher=Addison Wesley |isbn=0-201-11609-X |page=100 }}</ref> In regions of the electromagnetic spectrum in which absorption by the material is significant, it is related to the electronic absorption spectrum through the imaginary component of the complex refractive index. The electronic absorption spectrum of an opaque material, which is difficult or impossible to measure directly, may therefore be indirectly determined from the reflection spectrum by a [[Kramers-Kronig relations|Kramers-Kronig transform]]. The polarization of the reflected light depends on the symmetry of the arrangement of the incident probing light with respect to the absorbing transitions dipole moments in the material.

Measurement of specular reflection is performed with normal or varying incidence reflection spectrophotometers (''reflectometer'') using a scanning variable-wavelength light source. Lower quality measurements using a [[glossmeter]] quantify the glossy appearance of a surface in [[gloss units]].