Lambert's Laws

Lambert's First Law

The illuminance on a surface illuminated by light falling on it perpendicularly from a point source is proportional to the inverse square of the distance between the surface and the source.

Lambert's Second Law

If the rays meet the surface at an angle, then the illuminance is proportional to the cosine of the angle with the normal.

Lambert's Third Law

The luminous intensity of light decreases exponentially with distance as it travels through an absorbing medium.

See also: Illuminance.