Artemia franciscana is one of the most used organisms as live food to larvae of different marine species, so it is important to determine the appropriate food ration to improve its biochemical composition and maintain the nutritional stability of the Artemia. Furthermore, even though light is important in newly hatched nauplii, its effect in the late stages of Artemia have been poorly studied. This study aimed to evaluate the effect of food density (Chaetoceros muelleri microalgae) on the ingestion rate, protein, and lipid content of A. franciscana juveniles exposed and unexposed to light during 6 h. The experiment evaluated six treatments, resulting from combining three densities of C. muelleri as a food: 600,000, 900,000, and 1,200,000 cell mL-1 and two illumination conditions: exposed and unexposed to the light. The ingestion rate was evaluated at 3 and 6 h, while protein and lipid content at the end of the experiment. The highest ingestion rates were observed in the treatment of 900,000 cell mL-1 exposed to light at 3 h (253,118 cell ind-1 h-1) and unexposed to light at 6 h (164,712 cell ind-1 h-1). At the same time, the highest content of lipid (13.52 μg ind-1) and proteins (38.28 μg ind-1) per organism was obtained with the treatment of 900,000 cell mL-1 unexposed to light. There was an interaction between cell density and light since both factors influenced the results of the ingestion rate and lipid content of the juveniles of A. franciscana.