Diffuse reflection

Diffuse and mirror reflection ^[1]

Diffuse reflection from an uneven surface

The mechanism of diffuse reflection in an optically inhomogeneous solid

Diffuse reflection (from the Latin diffusio “propagation, spreading, scattering; interaction”) is the reflection of a light flux incident on a surface at which reflection occurs at an angle different from the incident one and not necessarily lying in the plane of the incident ray and normal to the surface ( mirror reflection).

Reflection becomes diffuse if surface irregularities are of the order of the wavelength (or exceed it) and are randomly located ^[2] . The criterion for surface roughness in reflection is the Rayleigh criterion:

{\ displaystyle h <{\ frac {\ lambda} {8 \ cos \ phi}},}

Where${\displaystyle \mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">h</span></span>}}$ {\ displaystyle h} - the height of the bumps;

${\displaystyle \mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">\lambda </span></span>}}${\ displaystyle \ lambda} - wavelength of incident light;

${\displaystyle \mathrm{<span\; class="mwe-math-element"><span\; class="mwe-math-mathml-inline\; mwe-math-mathml-a11y"\; style="display:\; none;">\varphi </span></span>}}${\ displaystyle \ phi} - angle of incidence to the surface.

The same surface can be matte, diffusely reflective for visible or ultraviolet radiation , but smooth and mirror reflective for infrared radiation . In the case of mixed light reflection, part of the radiation is reflected specularly , and part - diffusely.

Diffuse reflection from smooth surfaces is also possible if there are light scattering centers in the transparent medium of the surface material — heterogeneities, for example, polished white marble or milk surface.

In astronomy, it is numerically characterized by a reflection coefficient relative to a completely white body, the reflection of which is taken as 1, called the albedo .