The study of chemical reactions that are initiated or accelerated by exposure to visible light, ultraviolet radiation, or infrared radiation. The basic laws of photochemistry state that light must be absorbed by a compound for a chemical reaction to take place, known as the first or Grotthus–Draper law. The second or Stark–Einstein law states that for each photon of light absorbed by a chemical system, one molecule is activated for the subsequent reaction. It was derived by Albert Einstein during his development of the quantum theory of light. The Bunsen–Roscoe law of reciprocity states that a photochemical effect is directly proportional to the total energy dose, irrespective of the time required to deliver the dose.