Usually it is assumed that the absorbance decays exponentially with the time dependence of the photochemical kinetics. Although this is true in the limiting case of vanishing absorbance, deviations are to be expected for realistic samples, because the local photochemical kinetics slows down with increasing initial absorption and penetration depth of the radiation. We analyze the time dependence of the absorbance originating from photochemical first order kinetics of dye-doped systems and compare the data with experimental results published by Lafond et al. and Tork et al. for fulgides doped in different polymer matrices.