It was analyzed the difference of Drosophila life span in strains with low activity of Sod or excision repair enzyme Mus210 (homolog of yeast RAD4 and mammal XPC) in comparison with wild type strain Canton-S in conditions of 24 h and 0 h light. Mutants having low capacity to detoxify free radicals and repair DNA are characterized by stronger difference between life span at 24 h and 0 h light in comparison with wild type strain. Thus the life span increasing in the dark is due to decline of free radical and DNA lesions production. In wild type strain the effect of 12 h dusky light had not more effect on life span than intensive 24 h light. In most cases the difference between life span at 0 h and 24 h light was too much in males than in females, especially in Sod strain.