The contribution of the red luminescent component to the solar radiation transmitted through the light-transforming polyethylene films with 0.05-5% m/m additives of photoluminophore based on organic and inorganic europium compounds has been determined. The investigations into this field are connected with the study of factors determining a marked increase in the economical productivity of plants when cultivated under such films (polysvetan effect). The data obtained based on the spectra of solar radiation transmission and reflection by light-transforming films and the initial disperse photoluminophore have shown that the contribution of luminescent radiation in the region near 600 nm is 0.01-0.1% or 0.004-0.39 W/m2. In this case, the variations of transmission for the radiation in the same spectral region by light-transforming films due to uncontrolled reflection and scattering are two to three orders of magnitude greater than the contribution of the luminescent component. The data obtained do not confirm the hypotheses existing on the polysvetan effect by the action of the phytochromic mechanism of plants due to the enhanced portion of the red component in the transmitted solar radiation. The polysvetan effect may be an example of the low-energy photoluminescent biostimulation analogous to the known low-energy photoinduced biostimulation under the exposure to the red laser and LED radiation.