Photolytic decomposition reactions take place in the presence of light.
A photodecomposition reaction is a decomposition reaction wherein the reactant is broken down by absorbing energy from photons into its constituents. Since the analysis of a compound takes place using light energy or, in other words, photons, therefore, such reactions are called photolytic reactions.
Example: The decomposition of silver chloride into silver and chlorine is caused by light energy.
2AgCl → 2Ag + Cl2