Duckweed has been considered as a valuable feedstock for bioethanol production due to its high biomass and starch production. To investigate the effects of light conditions on duckweed biomass and starch production, Lemna aequinoctialis 6000 was cultivated at different photoperiods (12:12, 16:8 and 24:0 h) and light intensities (20, 50, 80, 110, 200 and 400 mu mol m(-2) s(-1)). The results showed that the duckweed biomass and starch production was increased with increasing light intensity and photoperiod except at 200 and 400 mu mol m(-2) s(-1). Considering the light cost, 110 mu mol m(-2) s(-1) was optimum light condition for starch accumulation with the highest maximum growth rate, biomass and starch production of 8.90 g m(-2) day(-1), 233.25 g m(-2) and 98.70 g m(-2), respectively. Moreover, the results suggested that high light induction was a promising method for duckweed starch accumulation. This study provides optimized light conditions for future industrial large-scale duckweed cultivation. (C) 2015 Elsevier Ltd. All rights reserved.