Lambertian Emitter

An emitter that radiates according to Lambert’s cosine law, which states that the radiance of certain idealized surfaces depends on the viewing angle of the surface. The radiant intensity of such a surface is maximum normal to the surface and decreases in proportion to the cosine of the angle from the normal. Given by:

N = N0cosA

N =  radiant intensity
N0 = radiance normal to an emitting surface.
A = angle between the viewing direction and the normal to the surface.