Editing Lambert's cosine law (section)

==Lambertian scatterers and radiators==

When an area element is radiating as a result of being illuminated by an external source, the [[irradiance]] (energy or photons /time/area) landing on that area element will be proportional to the cosine of the angle between the illuminating source and the normal. A Lambertian scatterer will then scatter this light according to the same cosine law as a Lambertian emitter. This means that although the radiance of the surface depends on the angle from the normal to the illuminating source, it will not depend on the angle from the normal to the observer. For example, if the [[moon]] were a Lambertian scatterer, one would expect to see its scattered brightness appreciably diminish towards the [[terminator (solar)|terminator]] due to the increased angle at which sunlight hit the surface. The fact that it does not diminish illustrates that the moon is not a Lambertian scatterer, and in fact tends to scatter more light into the [[oblique angle]]s than a Lambertian scatterer.

The emission of a Lambertian radiator does not depend on the amount of incident radiation, but rather from radiation originating in the emitting body itself. For example, if the [[sun]] were a Lambertian radiator, one would expect to see a constant brightness across the entire solar disc. The fact that the sun exhibits [[limb darkening]] in the visible region illustrates that it is not a Lambertian radiator. A [[black body]] is an example of a Lambertian radiator.