Thus, the intensity of illumination of the point is inversely proportional to the square of the distance from the source.
Lambert Cosine Law
It states that, "when light falls obliquely on a surface, the illumination of the surface is directly proportional to the cosine of the angle of incidence of light on the surface". It is used to find the illumination of a surface, when light falls on the surface along an oblique direction.
Suppose a light beam from a source S falling on a surface area A as shown in the figure. The normal to the surface makes an angle θ with the direction of light. Then, component of A normal to the direction of light ray is A cosθ.
Which is Lambert’s cosine Law, illumination of a surface is directly proportional to the cosine of the angle. The maximum illumination of a surface is obtained when light falls normally on the surface.
Hence illumination at a point due to a source is
- Directly proportional to luminous intensity of the source
- Inversely proportional to the square of the distance of the point from the source
- Directly proportional to the cosine of the angle of incidence of luminous flux.
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