Energy is transformed from the light reaction step to the dark reaction step by

Energy is transformed from the light reaction step to the dark reaction step by ATP.
The dark reaction occurs outside of the thylakoids. In this reaction, the energy from ATP and NADPH is used to fix carbon dioxide (CO₂). The products of this reaction are sugar molecules and other organic molecules necessary for cell function and metabolism.
ATP can be used to store energy for future reactions or be withdrawn to pay for reactions when energy is required by the cell. Plants capture and store the energy they derive from light during photosynthesis in ATP molecules.