Attenuation of Light

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.