Beers Law

 
                                                      Transmittance VS. Absorbency

     Conceptually, the Tansmittance is an easier quantity to understand than the Absorbance. If T = 30%, then 30% of the photons passing through the sample reach the detector and the other 70% are absorbed by the analyte. The absorbance is a slightly less intuitive quantity. If A = 0, then no photons are absorbed. If A = 1.00, then 90% of the photons are absorbed; only 10% reach the detector. If A = 2.00, then 99% of the photons are absorbed; only 1% reach the detector. It is the absorbance, however, that displays a simple dependence on the concentration and cell path length (Beer's Law), and thus most chemists choose to report data in terms of absorbency rather than transmittance.