Light dependent reactions require an actual source of light, and this is from the sun, for energy to carry out the first stage of photosynthesis. They need solar energy to split a water molecule in order to obtain electrons from hydrogen to be used in fueling photosynthesis. Light independent reactions do not require a light source for energy but rather they use energy that was created by the light dependent reactions to complete the process of photosynthesis in which different carbohydrates for the plant are made.