A quarter of a century after establishment of inhibitory effect of blue light on growth of cancer cells, many aspects of mechanism of photophysical and photochemical processes underlying the effect of above physical factor have been quite well studied. However, the most controversial question remains about molecules-acceptors of optical radiation. Important information about possible participation of particular endogenous compound in the implementation of photobiomodulation effect can be obtained from comparison of its absorption spectrum and spectrum of action of optical radiation on cells. In this regard, we studied the spectral dependence of light-induced changes in metabolic activity of HeLa cells as well as the dependence of ROS level formation in cells when exposed to radiation from LED sources, peaking at λmax = 395, 405, 415, 445,465 nm, in the energy dose range of 1.5-15.0 J/cm2. It has been shown for the first time that inhibitory effect of blue light as well as the level of light-induced ROS formation decrease with increasing wavelength of applied radiation. A new pattern has been established, consisting of change in the contribution of various types of ROS to photobiological effects recorded at different time intervals after the cessation of cell irradiation.