Circadian rhythms and light: Effects on health and performance

A general view on circadian system structure and performance is provided for a better understanding of the problems derived from its malfunction and the ways to compensate for the negative effects using light therapy. The relevance of exposure to light-darkness cycles, in order to synchronize the circadian system, is highlighted and the reasons behind night-shift workers ill health are explained. Differences between circadian and visual stimulation are given which relates to the reasons why standard photometry does not provide accurate measurements for the optimum stimulation of the circadian system. Finally, the philosophy of light therapy and its efficacy in avoiding/eliminating problems associated with inaccurate circadian system functioning in reference to (1) its transitory activation, (2) biological and chronological clocks mismatches and (3) seasonal depression, are described.