Green plants obtain usable energy from the sunlight during light-dependent reactions of photosynthesis. During the light reactions which takes place in the thylakoid of chloroplasts, chlorophyll molecules absorb sunlight and covert light energy into assimilatory power that includes ATP and NADPH (nicotinamide adenine dinucleotide phosphate). Photolysis of water also takes place during light dependent reactions. The assimilatory power ( ATP + NADH) provides energy for the reduction of carbon dioxide during Calvin cycle of photosynthesis.