Chemical as well as physical property that may occur under the influence of light is called Photochemistry. Photochemical transformations have two fundamental principles. According to first law photochemical reaction initiated when molecule or compound absorb photon, this law is discovered by Grottuss- Draper. The second law gives a photo equivalence law. This law given by Stark-Einstein. Quantum Yield (Φ) calculates the efficiency of photochemical reaction. Many photochemical reactions are categorized as complex reaction, thus for a particular event the quantum yield is specified. It represented by a formula as “ratios of disappearance of reactant to number of moles of a product appear, on absorption of one mole of light by compound." After that many of secondary reactions proceeded (shown in the gray box). Absorption of light (uv/vis) induces energy sufficient in molecule to break covalent bonds. Since, E = hc / λ, hence, longer wavelength have less energy and vice-versa. Consequently, ultraviolet light is most effect photochemical reactions. In this review we discuss about amongst all some of photochemical reactions collectively which are initiated by ultraviolet light specifically.