When the monochromatic light passes through a random attenuating medium, the radiant intensity drops exponentially with the length of the path and attenuation coefficient. The law of exponential decay was called the law of Bouguer, Lambert, Beer or some combination of these three. Here we refer to it as the modified Beer–Lambert law due to the arrangement proposed in the current work. This work aims to use UV–Vis spectroscopy and apply Beer–Lambert law; the feasibility of the work is assessed and shows the possibility of validating a beam intensity measurement experiment in two experimental situations with a known constant. The empirical part of the work consists of changes in chemical or physical properties. The first experimental situation consists of the variation of the concentration of the medium and evaluates the absorption of the laser beam. In this situation is used industrial synthetic dye. The second experiment also assessed the absorption of laser intensity, using variations of the number of films poly (ethylene terephthalate) polymeric sums found in the PET bottle. The values found for constant were ≈ 2.697 in the variation of concentration of synthetic dye in blue color, and for the condition of PET, films were found and ≈ 2.699. The value of the constant experimentally found approaches the Euler number. And they are so, proving that the Euler number can be determined experimentally in a system of Markovian non-interagent particles and how to experimentally validate a result by the association of a constant known in the literature.