It indicates that there is a linear relationship between the absorbance and the concentration of a sample. For this reason, Beer's law can only be applied to the linear relationship. Beer's law written as follows: [A=ϵlc] where A is the measure of absorbance, ϵ is the molar extinction, the coefficient or molar absorptivity (or absorption coefficient), l is the path length and that is concentration. The molar extinction coefficient is given as a constant and varies for each molecule. Since absorbance has no units, the unit of ϵ must cancel the units of length and concentration. Therefore ϵ has the units L•mol-1•cm-1. Path length is measured in centimeters. Since a standard spectrometer uses a 1 cm wide cuvette, l is always assumed to be 1 cm. Since the absorption, ϵ and path length are known, we can calculate the concentration c of the sample (Chang Raymond, 2005). The Beer-Lambert law relates the attenuation of light to the properties of the material through which the light is transmitted.