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What are Lambert's Laws?

Asked by: Annemarie Straube


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

2. If the rays make an angle x with the normal to the surface, the illuminance is proportional to cos(x).

3. (Also called Bouquer’s law) The luminous intensity (I) of light decreases exponentially with the distance d that it enters an absorbing medium i.e. I = Io exp(-z d)

Where Io is the intensity of the radiation that enters the medium and z is its linear absorption coefficient. These laws were first stated (for light) by Johann H. Lambert.

Answered by: Dan Summons, Physics Undergrad Student, UOS, Souhampton

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