*Photosynthesis: Plants use solar energy to convert carbon dioxide and water into glucose and oxygen.
*Human formation of vitamin D by exposure to sunlight.
*Bioluminescence: e.g. In fireflies, an enzyme in the abdomen catalyzes a reaction that produces light.
*Polymerizations started by photoinitiators, which decompose upon absorbing light to produce the free radicals for radical polymerization.
*Photodegradation of many substances, e.g. polyvinyl chloride and Fp. Medicine bottles are often made from darkened glass to protect the drugs from photodegradation.
*Photochemical rearrangements, e.g. photoisomerization, hydrogen atom transfer, and photochemical electrocyclic reactions. 
*Photodynamic therapy: Light is used to destroy tumors by the action of singlet oxygen generated by photosensitized reactions of triplet oxygen. Typical photosensitizers include tetraphenylporphyrin and methylene blue. The resulting singlet oxygen is an aggressive oxidant, capable of converting C–H bonds into C–OH groups. 
*Diazo printing process
*Photoresist technology, used in the production of microelectronic components. 
*Vision is initiated by a photochemical reaction of rhodopsin.
*Toray photochemical production of ε-caprolactame.
*Photochemical production of artemisinin, an anti-malaria drug.
*Photoalkylation, used for the light-induced addition of alkyl groups to molecules.
*DNA: photodimerization leading to cyclobutane pyrimidine dimers.