This article analyzes how absorption of light by suspensions of phototrophic bacteria is modulated by changes in the biomass of the culture, the size of the culture vessel and by the presence of refractile structures within the cells. Increases in biomass and culture size result in higher rates of light absorption but in the decrease of the amount of energy available per cell. The presence of refractile structures has different consequences depending on the biomass concentration. In dense cultures, the accumulation of refractile structures increases the reflection of light, and also reduces specific light absorption. In diluted cultures, however, the effect is the opposite, and refractile structures seem to increase light absorption
