Analysis of the photosynthetic irradiance curves (IC), and action and quantum efficiency spectra on the basis of the model of Kok ei al. (1970) showed that under a low irradiance all ÍC, irrespective of sample absorbances, had non-linear (exponential) parts. Under a high irradiance, the IC (especially those of higher situated sublayers) showed "saturation", which was expressed as a decrease in the dechne of the curves. The IC non-linearity was reflected in the shape of the photosynthetic action spectra (AS). Under a low irradiance, the AS showed a decrease (drop) in the spectral regions with low absorbances, i.e. between 500 and 650 nm, as well as above 690 nm (Emerson s "red drop effect"). On the contrary, under higher irradiances an increase in quantum esfficiency (QE) in the same regions was well-expressed. When IC were non-linear, exact estimation of the photosynthetic AS and QE was much complicated and respective results should be accepted with a fair approach to accuracy.