Chemiosmosis drives ATP synthesis in the light reactions by coupling proton movement through ATP synthase to the phosphorylation of ADP. In chloroplasts, the process is also called photophosphorylation because the proton gradient is ultimately created by light-powered electron transport.
As electrons move through the photosynthetic chain, the cytochrome b6f complex contributes to proton transfer from the stroma into the thylakoid lumen. Water oxidation at photosystem II also adds protons to the lumen. These actions create an electrochemical gradient across the thylakoid membrane, with a high proton concentration inside the lumen.
Protons then flow back toward the stroma through the membrane portion of ATP synthase, called CF0. Their movement drives rotation and conformational changes in the CF1 catalytic portion, enabling ATP formation from ADP and inorganic phosphate. The resulting ATP and NADPH support carbon fixation.
Chemiosmosis is the mechanism, whereas ATP synthase is the enzyme that directly makes ATP. Electron transport helps establish the gradient, but it is not itself the name of the proton-driven coupling process. Peter Mitchell proposed the chemiosmotic hypothesis in 1961 and received the 1978 Nobel Prize in Chemistry.