Improved fiber quality has given US cotton (Gossypium hirsutum L.) producers a competitive edge in the world cotton markets. However, cotton grown under lower light conditions has been shown to exhibit reductions in the quality of the lint produced. Under these conditions, the full genetic potential for these improved fiber qualities is often not attained. Intuitively, one might assume that reduced photosynthate production is the underlying cause of this phenomenon, but, considering the number of cellular processes affected by light that have been identified, there may be more that is involved. The objectives of this study was to determine how the carbohydrate (starch, glucose, fructose, and sucrose) concentrations of the fiber at various stage of development were altered by varying the light level during boll development for three genotypes differing in fiber quality.