This work characterizes the influence of different levels of available sunlight in the photosynthetic apparatus of chestnut leaves from the opposite canopy sides (North and South) and also the transition sides (East and West). During daylight, significant variations on radiation were measured around the canopy. The North side is always a shady side (only 10-15% of total sunlight is available for chloroplast energization) and in the other side there is a full light availability during all the daylight. East is a sunny side during the morning and a shady one during the afternoon; the opposite occurs on the West side. The photosynthetic rates are 15, 26 and 19% of the maximal photosynthesis in East, South and West at 10, 13 and 16h, respectively. Photosynthesis was significantly influenced by the gradual temperature increase decreasing about 27% during the day (between 24 and 30°C from 10 to 16h)' suggesting that the optimal temperature for chestnut must be under 28°C. This information is also supported by a study in thylakoid potential generation, where maximal potential occurred at 16 and 20°C in North and South side, respectively. Fruits were also studied, the North fruits being 13% smaller and 5% lower in starch.