Assessing the effect of light pollution, Microcystis aeruginosa was grown with and without low levels of night lighting. Significant differences were observed between the treatments in the maximum quantum yield of charge separation, the intracellular chlorophyll a concentration, the functional absorption cross-section of photosystem II, the number of Rubisco per cell and per chlorophyll a, the number of photosystem I per chlorophyll a, and the chlorophyll a fraction not bound to the photosystems and IsiA.