Combined dark and photo-fermentation of ground wheat starch was carried out by using different light sources, intensities and lighting regime. A mixture of heat treated anaerobic sludge and Rhodobacter sphaeroides-RV with a certain light/dark bacteria ratio was used in batch experiments. Tungsten, fluorescent, infrared (IR), tungsten + infrared, halogen lamps were used as light sources with a light intensity of 270 Wm(-2) along with sunlight. Halogen lamp was found to be the most suitable light source yielding the highest cumulative hydrogen formation (178 ml) and yield (218 ml g(-1) starch). Combined fermentations were performed at different light intensities (1-10 klux) using the halogen lamp in the second set of experiments. The optimum light intensity was found to be 10 klux (approx. 352 Wm(-2)) resulting in the highest cumulative hydrogen (ill ml) and hydrogen yield (139 ml H(2) g(-1) starch). Hydrogen formation was limited by the availability of light at low light intensities below 10 klux. Durations of dark/light cycles were changed to determine the most suitable lighting regime. Hydrogen gas formation increased with increasing cycle time and continuous lighting resulted in the highest cumulative hydrogen formation and hydrogen yield. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved