EM radiation impinging a rough surface is (partly) reflected back (scattering). When the the sine of the angle of incidence of the radiation is equal to the sine of the angle of reflection, sin(øi) = sin(ør), then the surface behaves like a mirror (Snell's Law). Furthermore, a surface is defined as a “perfect mirror” (Fig.1) if all the incident radiation is reflected in that direction saving its original intensity. A surface is defined as “Lambertian diffuser” or “isotropic reflector” (Fig. 2), when the radiation is reflected in all directions with the same intensity. A surface is defined as “perfect Lambertian” when all the incident radiation is reflected isotropically (i.e. not-absorbing, not-transmitting surface). A surface is defined as "almost Lambertian" (Fig.3) if the reflection does not occur in an exactly isotropic way but according to privileged directions. “Perfect mirrors” as well as “perfect Lambertian” surfaces describe ideal bodies, while natural bodies behave like “almost Lambertian” surfaces with a preferred reflection direction around the one established by the sines reflection law.