If the radiation is especially intense, nonlinear optical processes can also cause variances. The main reason, however, is that the concentration dependence is in general non-linear and Beer's law is valid only under certain conditions as shown by derivation below. For strong oscillators and at high concentrations the deviations are stronger.
The impact of radiation intensity on optical processes can lead to variations, particularly when the concentration dependence is nonlinear. This non-linearity makes Beer's Law less accurate at high concentrations or for strong oscillators.