An in-depth investigation of how various illumination conditions influence microalgal growth in photobioreactors (PBR) has been presented. Effects of both the light emission spectrum (white and red) and the light incident angle (08 and 608) on the PBR surface were investigated. The experiments were conducted in two fully controlled lab-scale PBRs, a torus PBR and a thin flat-panel PBR for high cell density culture. The results obtained in the torus PBR were used to build the kinetic growth model of Chlorella vulgaris taken as a model species. The PBR model was then applied to the thin flat-panel PBR, which was run with various illumination conditions. Its detailed representation of local rate of photon absorption under various conditions (spectral calculation of light attenuation, incident angle influence) enabled the model to take into account all the tested conditions with no further adjustment. This allowed a detailed investigation of the coupling between radiation field and photosyn-thetic growth. Effects of all the radiation conditions together with pigment acclimation, which was found to be relevant, were investigated in depth.