Involved in repair of UV radiation-induced DNA damage. Exhibits specific, light-dependent repair activity for a cyclobutyl pyrimidine dimer by catalyzing the light-dependent monomerization (300-600 nm) of the dimers (in cis-syn configuration), which are formed between adjacent bases on the same DNA strand upon exposure to ultraviolet radiation. It has been shown that photorepair is more important than excision repair for UV-induced DNA lesions in Synechocystis. Its disruption does not affect circadian rhythm. cyclobutadipyrimidine (in DNA) = 2 pyrimidine residues (in DNA). Binds 1 FAD per subunit. Binds 1 coenzyme F420 non-covalently per subunit. Monomer. Belongs to the DNA photolyase class-1 family.