Lambert Law

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Lambert Law

A law of physics which states that the radiant intensity (flux per unit solid angle) emitted in any direction from a unit radiating surface varies as the cosine of the angle between the normal to the surface and the direction of the radiation. The radiance (or luminance) of a radiating surface is, therefore, independent of direction. Also called Lambert cosine law. Compare cosine law of illumination. </dd>
Lambert law is not obeyed exactly by most real surfaces, but an ideal black body emits according to this law. This law is also satisfied (by definition) by the distribution of radiation from a perfectly diffuse radiator and by the radiation reflected by a perfectly diffuse reflector. In accordance with Lambert law, an incandescent special black body when viewed from a distance appears to be simply a uniformly illuminated disk. This law does not take into account any effects that may alter the radiation after it leaves the source. </dd>


This article is based on NASA's Dictionary of Technical Terms for Aerospace Use