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
'For the sake of persons of ... different types, scientific truth should be presented in different forms, and should be regarded as equally scientific, whether it appears in the robust form and the vivid coloring of a physical illustration, or in the tenuity and paleness of a symbolic expression.'