Microalgae have been recently recognized as tools for high value products like polyunsaturated fatty acids, pigments or polysaccharides. So far however, only little modelling work has been done. Modelling of kinetics in standard photo-bioreactors is difficult because of strong light gradients and the lack of control of light Bur. For the study of microalgae kinetics and for modelling purposes a new kind of photo-bioreactor has been designed. Model based approaches are used to optimize illumination and to achieve higher light intensities and a more uniform illumination. With the aid of the new reactor, kinetics of microalgae growth and product formation can be investigated under controlled conditions.