Spectrally Selective Transformations of Solar Radiation by Retinal Photoreceptors in the Control of the Circadian Rhythm of the Human Body throughout an 11-Year Cycle of Solar Activity

Abstract—The round-the-day effect of solar radiation on photoreceptors of the retina of the eye and its role in the control of the circadian rhythm of the human body within an arbitrary 11-year cycle of solar activity are considered. Processed data describing the variation of the spectral and energy characteristics of solar radiation that reach the Earth’s surface over a solar activity cycle are given. On this basis, a generalized analytical expression has been obtained that models the spectrally selective processing of the sum of the direct and diffuse components of solar radiation by retinal rods and blue-sensitive (S type) cones. The obtained expression allows consideration of separate spectrally selective processing of the direct and diffuse components of solar radiation by rods and S cones of retina, including the case of a catastrophic lesion of one of the neuronal paths that connect rods or S cones with suprachiasmatic hypothalamus nuclei. It is shown that the effective spectrum obtained as a result of spectral selection of the components of solar radiation that is used to control the circadian activity of the human body is determined solely by the spectral sensitivity of rods and S cones. The effective spectrum does not depend on daily variations in the spectrum of solar radiation as the angular elevation of the Sun varies; the daily energy characteristics of the effective spectrum, which vary within each solar activity cycle, retain their dependence on the Sun’s elevation in the daytime and on the current phase of the solar activity cycle. Significant changes in the characteristics of solar radiation within the cycle of solar activity infer that it is necessary to take them into account in studying and modeling the control processes of human circadian activity driven by solar radiation.