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The quantitative studies with organisms of different complexity (HeLa cells, yeast organisms, E coli bacteria) to prove or disprove the stimulating action of low-intensity visible light are presented. The stimulation of DNA synthesis in HeLa cells was observed for four spectral intervals with maxima at near 400, 620, 680 and 760 nm. The red light stimulates the growth of yeast (Saccharomycodes ludwigii) and E coli in exponential growth phase. The action spectrum of monochromatic light on the growth of these organisms in the red region is very similar to that for HeLa cells.

The reproduction rate and protein synthesis of the yeast-like fungus Endomyces magnusii and yeast Torulopsis sphaerica was studied after the He–Ne laser (λ = 632.8 nm) irradiation. The synthesis of protein in E. magnusii was activated in dose range from 0.42 to 0.84 J/cm2 with maximum at 0.63 J/cm2. In T. sphaerica the maximal activation took place at 0.42 J/cm2. The lag-period was not changed, but the exponential period of the growth was reduced by 1.5 hours for irradiated cells.