The light energy strikes the leaf, passes into the leaf and hits a chloroplast inside an individual cell. The light energy, upon entering the chloroplasts, is captured by the chlorophyll inside a grana. The oxygen is released into the air. The hydrogen is taken to the stroma along with the grana's remaining light energy.
Carbon dioxide enters the leaf and passes into the chloroplast.
In the stroma the remaining light energy is used to combine hydrogen and carbon dioxide to make carbohydrates.