The conversion of light energy to chemical energy first occurs when electrons are transferred from excited photopigments to an electron carrier in a photosystem (pigments together with proteins organized into complexes and located in the thylakoid membranes of chloroplasts).
The light-dependent reactions is one of the two successive phases that occur during photosynthesis (other is light-independent reactions). The light-dependent reactions use sunlight energy (electromagnetic radiation) to make the energy storage molecule ATP and the reduced electron carrier NADPH. In the light-independent reactions (also called Calvin cycle), CO2 is absorbed and fixed in order to build three-carbon sugars (glyceraldehyde-3-phosphate) and this process is fueled by, ATP and NADPH from the light reactions.