Our study showed that the effect of light on germinating spores of Streptomyces was variable: some species were indifferent, whereas others, such as Streptomyces viridosporus, displayed a marked inhibition of CFU numbers on growth medium. A special study with S. viridosporus showed that light only had an impact during the first few hours of spore incubation. The effects of scavengers of toxic forms of oxygen and of photosensitizers, along with the oxidative stress of illuminated spores evidenced by the superoxide dismutase levels, suggested that light and oxygen had a combined action.