a reduction in the intensity of a light beam as the beam propagates in matter owing to the joint action of the absorption and scattering of light.
In the general case, the attenuation of a beam with an initial intensity of I0 may be calculated on the basis of the Bouguer-Lambert-Beer law: I = I0e–βl, where e is the thickness of the absorbing substance and β = α + ρ is the attenuation coefficient, which is equal to the sum of the absorption coefficient α and the scattering coefficient ρ.
The attenuation coefficient is measured in some reciprocal unit of length, for example, m–1 or cm–1. The attenuation constant, a dimensionless factor, is equal to the sum of the absorption factor and the dimensionless ratio of the luminous flux scattered by a medium to the flux incident on the medium.
As a rule, attenuation coefficients and attenuation factors are different for different wavelengths.
L. N. KAPORSKII