Before going into the detail of the light dependent reaction, some points have to be made clear about the light dependent phase: The Light-dependent reaction of photosynthesis takes place in the thylakoids of the chloroplast. Two major processes take place § ATP and NADPH are formed. § Splitting of the water molecule (photolysis) takes place to give oxygen. · The ATP and NADPH formed in the light reaction are utilized to form carbohydrate in the dark reaction. So, what should be the first step of the light reaction ? The absorption of light (duh!) The light reaction begins with the absorption of light in the thylakoids . Now , you may think that why is light absorption possible only in the thylakoids ? It is because the thylakoids have two very hard working friends that make it possible , each of which is called a photosystem (PS680 AND PS700). They are embedded in the thylakoid membrane and absorb light