Incident light was manipulated in large plankton towers containing algae, microbes, and herbivores. Paradoxically, food chain production was lower with greater light energy input. This apparent paradox is resolved by recognizing stoichiometric constraints to food chain production. At high light, elevated algal biomass was achieved mainly by increases in cellular carbon. Consumers have a high phosphorus demand for growth, and thus a large excess of carbon inhibited, rather than stimulated, their growth. These experiments may help us predict the consequences of anthropogenic perturbations in nutrients, carbon, and solar energy. They also may help us to understand the wide range of consumer biomass and production at a given level of primary productivity in ecosystems.