This self-study module is part of the series ‘Introduction to Plant Biology’ and introduces the light-dependent reactions of photosynthesis and their role in converting light energy into chemical energy. It is designed for students studying basic plant biology and for teachers seeking clear explanations and illustrative figures for educational use. The module explains the two photosynthetic reactions: light-dependent and light-independent, with a focus on the processes occurring in the chloroplast during the light-dependent phase. Students explore the formation of the energy carriers ATP and NADPH, the splitting of water into oxygen, and the role of fluorescence as an indicator of disturbances in the photosynthetic process and therefore plant health.