Definitions Lambertian Reflection Dull, matte surfaces can be modeled by Lambertian surfaces and are said to exhibit Lambertian reflection , or diffuse reflection . The assumption is that these surfaces reflect light with equal intensity in all directions, and hence appear equally bright from all directions. Beam of infinitesimal cross sectional area dA at angle of incidence intercepts area of Let us examine the reason behind having such a model. There are two factors which needs attention here.
Intensity is energy per unit area.
This impinges an area of screen. Thus intensity on screen is . We must also consider the amount of light seen by the viewer. Lambertian surfaces have the property, often known as Lambert's law, that the amount of light reflected from a unit differential area dA toward the viewer is directly proportional to the cosine of the angle between the direction to the viewer and . Since the amount of surface area seen by the viewer is inversely proportional to the cosine of this angle, these two factors cancel out.