The fraction of light incident on a surface that is reflected and varies according to the wavelength distribution of the light.

In certain fields, reflectivity is distinguished from reflectance by the fact that reflectivity is a value that applies to thickreflecting objects. When reflection occurs from thin layers of material, internal reflection effects can cause the reflectance to vary with surface thickness. Reflectivity is the limit value of reflectance as the surface becomes thick; it is the intrinsic reflectance of the surface, hence irrespective of other parameters such as the reflectance of the rear surface.

The reflectance spectrum or spectral reflectance curve is the plot of the reflectivity as a function of wavelength.

See Profiling for UV.