Beer’s law tells us how the amount of electromagnetic radiation absorbed by a sample is related to the concentration of the absorbing species. Beer’s law tells us that the absorbance is equal to the length of the sample, l, times the concentration, c, of the absorbing species in the sample, times the molar absorptivity coefficient, ε, of the species.

In this equation A is absorbance, which is defined as the negative of the logarithm of the ratio of the intensity of light passing through a sample to that incident on it. Basically, this gives us a measure of how much light a sample is absorbing and how much light is passing through it.