the amount of light absorbed by a sample is dependent on the concentration of the pigment in the sample (C) , path lenght l, and the extinction coefficient of the pigment E.
Determining the amount of monochromatic light absorbed by a substance is most-commonly used to determine the concentration of that substance in a sample. the concentration C of a substance in a sample is one of three factors that affect the amount of light absorbed by a sample. the other two are path lenght (l), that is the distance the light travels through the sample, and the extinction coefficient of the absorbing substance (E), the extinction coefficient is simply a measure of how strongly a substance absorbs light of a given wavelenght. the relationship between transmittance or absorbance and these three factors is expressed by Beer's Law , one of the fundamental laws of spectrophotometry . Beer's law states that the intensity of transmitted light decreases exponentially as each of these three factors increases. that is,