Important Materials Theory - Photographic Rendering with V-Ray for SketchUp - page 247

Light and material interaction - what is
reflectivity?
In discussing only the color or diffuse aspect of light reflection (reflectance) in our ma-
terials, we have so far neglected to mention that surfaces often have physical proper-
ties that can cause light to reflect off them in a very different manner. This change in
light behavior causes it of course to produce a very different visual result.
In computer graphics, the Lambertian model for diffuse reflection (reflectance) of light
describes a perfectly uniform micro-faceted (or rough) surface that diffuses or scat-
ters light equally in all directions. Whenever we discuss a surface in terms of its color
alone, (what we might call a matte surface, for example) it is generally this kind of re-
flectance model that we have in mind.
Note
Lambertian reflectance is named after Johann Heinrich Lambert, who introduced
the concept of perfect diffusion in his 1760 topic Photometria , a publication that is
in fact still available in paperback even today.