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.