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(February 2008)| In optics, the Beer–Lambert law, also known as
Beer's law or the Lambert–Beer law or the Beer–Lambert–Bouguer
law (named after August Beer, Johann Heinrich Lambert, and
Pierre Bouguer) relates the absorption of light to the
properties of the material through which the light is
travelling. The law states that there is a logarithmic
dependence between the transmission (or transmissivity), T, of
light through a substance and the product of the absorption
coefficient of the substance, α, and the distance the light
travels through the material (i.e., the path length), ℓ. The
absorption coefficient can, in turn, be written as a product of
either a molar absorptivity (extinction coefficient) of the
absorber, ε, and the molar concentration c of absorbing species
in the material, or an absorption cross section, σ, and th