UV radiation induced two major classes of pyrimidine dimmers:the pyrimidine (6-4) pyrimidone photoproduct (6-4 product) and the cyclobutane pyrimidine dimmer(CPD).

• 紫外光照射可导致生物体产生两种损伤：(6-4)光产物和环丁烷嘧啶二聚体。