Light is one of the most important resources for plant. Light level in canopy varies greatly. Previous research using individual leaf shading showed no photosynthetic response to reduce light environment to main stem leaves. Our objective was to determine photosynthetic response of main stem, sympodial, and monopodial leaves to differential growth light environment. We monitored light environment on leaf surface and measured photosynthesis rates at different leaf ages. As leaf aged, light environment of main stem leaves slightly decreased while for sympodial and monopodial leaves it rapidly decreased. Pmax for main stem and sympodial leaves rapidly decreased with increasing leaf age. That significant decline in Pmax (70%) of main stem leaves was associated with non-significant reduction in leaf light environment indicated physiological response caused by leaf aging. Finally, the positive correlation between Pmax and differential light environment suggest photosynthetic adaptation of cotton leaves to growth light environment, in addition to physiological changes with leaf aging.