This study proposes lumostatic operations using a specific light uptake rate (q(e)) as a control parameter in order to maintain a desirable light condition. As a model system, bubble column photobioreactors have been operated lumostatically for photoautotrophic cultivations of Haematococcus pluvialis. Lumostatic operations were conducted at three levels of specific light uptake rates (q(e) = 1.5 x 10(-8), 3 x 10(-8), and 4.5 x 10(-8) muE cell(-1) s(-1)) and compared with constant light energy supply (I-0 = 40, 90, and 140 muE m(-2) s(-1)). In the case of the lumostatic operation at 4.5 x 10-8 muE cell(-1) s(-1), the cell concentration was enhanced over 250% than that obtained under constant light energy, without inducing astaxanthin accumulation. For the lumostat at q(e) of 3.0 x 10(-8) muE cell(-1) s(-1), the cell concentration increased almost 200% than that of the control experiments. These results indicate that a specific light uptake rate can be a useful parameter for lumostatic operation of photobioreactors and that the productivity of vegetative stage can be greatly improved by regulating the light condition based on the specific light uptake rates. (C) 2003 Elsevier Inc. All rights reserved.