Beer-Lambert
Law is the linear relationship between absorbance and concentration of an
absorbing species. The general Beer-Lambert law is usually written as:

A = a() * b * c

where
A is the measured absorbance, a() is a
wavelength-dependent absorptivity coefficient, b is the path length, and c is
the analyte concentration. When working in concentration units of molarity, the
*Beer-Lambert law* is written as:

A = * b * c

Where
is the wavelength-dependent molar
absorptivity coefficient with units of M^{-1} cm^{-1}. Data are
frequently reported in percent transmission (I/I_{0} * 100) or in absorbannce
[A = log (I/I_{0})].

Experimental
measurements are usually made in terms of transmittance (T), which is defined
as:

T = I / I_{o}

where
I is the** **light intensity after it passes through the sample and I_{o}
is the initial light intensity. The relation between A and T is:

A = -log T = - log (I / I_{o}).