Lambert surface

For opaque materials, the reflectance p is the complement of the absorptance. The directional distribution of the reflected radiation depends on the material, its degree of roughness or grain size, and, if a metal, its state of oxidation. Polished surfaces of homogeneous materials reflect speciilarly. In contrast, the intensity of the radiation reflected from a perfectly diffuse, or Lambert, surface is independent of direction. The directional distribution of reflectance of many oxidized metals, refractoiy materials, and natural products approximates that of a perfectly diffuse reflector. A better model, adequate for many calculational purposes, is achieved by assuming that the total reflectance p is the sum of diffuse and specular components p i and p. ... 

So-called Lambert surfaces, which emit or reflect with an intensity independent of angle approximately satisfied by most nonmetalbc, tarnished, oxidized, or roi surfaces. 

P.J. Goddard, and R.M. Lambert, Surface crystallography of rubidium on Ag( 111) and the chemical reactivity of nitric oxide on rubidium-dosed silver, Surf. Sci. 79, 93-108 (1979). 

R.M. Nix and R.M. Lambert. Surface Crystallography and Growth Modes of Rare Earth Metals and Alloys on Single Crystal Copper Nd on Cu(OOl). Surf. Sci. 186 163 (1987). 

Purely diffuse reflection occurs at microscopically irregular surfaces, while purely specular reflection occurs when the surface is perfectly smooth, like a minor. If the reflected radiance from a surface is completely uniform with angle of observation, it is called a Lambert surface. The BRDF for a Lambert surface is independent of both the direction of incidence and the direction of observation. Then, the reflectance simplifies to p(v, —h, = where pi is the Lambert reflectance. Specular reflection from and transmission throngh a smooth dielectric surface can be calculated from Snell s law and Fresnel s equations, given the optical constants of air and the dielectric material. 

Perfect diffuser n. Theoretical ideal white substance which reflects 100% of the incident light in a perfectly diffuse way official CIE reference white to which colors being measured are compared a Lambert surface, following the Lambert cosine law perfectly. 

For the special case of a Lambert surface, where p is a constant, p can be evaluated analytically. 

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