Comparative  studies  of  the  effect  of  radiation  from  laser  and  LED  sources  with  the  wavelength of λ = 405 and 445 nm on the metabolic activity of cultured somatic cells were performed. A more pronounced inhibitory effect is observed when exposed to light with λ = 405 nm. The absence of fundamental differences in the action of monochromatic and quasi-monochromatic light is noted. It is shown that the photobiological effect is due to photochemical processes involving various reactive oxygen species, whose contribution to the effects of cell inactivation depends on the time after the termination of irradiation. Porphyrin components were registered for the first time in the fluorescence spectra of the suspension of living cells along with the flavin component. Based on a comparison of the absorption characteristics of flavin and porphyrin sensitizers, as well as data from chemiluminescence analysis and the biological effects of radiation with λ = 405 and 445 nm, it is concluded that the determining contribution to the formation of singlet oxygen in cells when exposed to radiation with λ = 405 nm is made by endogenous porphyrins, characterized by the most intense absorption in this area. The contribution of flavins is more pronounced under the action of radiation with λ = 445 nm, corresponding to the maximum in their absorption spectrum and the minimum absorption of endogenous porphyrins.