The effects of light intensity (0-225 mu mol m(-2) s(-1)) on oxygen distribution, lipid production and biological community structure of algal-bacterial granules were investigated in six identical photo-sequencing batch reactors (with a dark/light cycle of 12 h/12 h). Typically green algal-bacterial granules could be developed at a light intensity of >= 135 mu mol m(-2) s(-1). The lipid content was significantly increased under higher light intensity, while the percentage of saturated fatty acid methyl esters was remarkably decreased. Results showed that light intensity >= 90 mu mol m(-2) s(-1) yielded enough O-2 production from algae, creating aerobic/anoxic zone (0.3-0.6 mg-O-2/L) in the core of granules and thus efficient algal-bacterial symbiosis system. Enhanced nitrogen and phosphorus removals were achieved in the reactors with stronger light illumination, probably attributable to the enrichment of ammonia oxidizing bacteria (Comamonadaceae and Nitrosomonadaceae) and algae (Navicula and Stigeoclonium). Illuminance >= 180 mu mol m(-2) s(-1) was found to be unfavorable for Nitrospiraceae.