A law governing the angular dependence of emitted or reflected radiation from an idealised surface. The radiation emitted from or reflected by a surface obeying Lambert's law is unpolarized and has a radiance that is constant with angle, or isotropic. Such surfaces are variously termed Lambertian or diffuse surfaces, reflectors, or emitters. They may also be termed perfectly diffusing radiators or reflectors. This law is sometimes called Lambert's cosine law to distinguish it from the Bouguer–Lambert law.