The Human Circadian System
This chapter analyses the human circadian system in detail, with particular attention to the effects of light. From a lighting design-oriented perspective, it presents the results of the main research, applied to lighting or developed in the physiological medical field, with reference to the non-image forming (NIF) effects produced by artificial lighting on the human organism. These effects primarily affect the regulation of melatonin production, which is the main marker of the state of the human circadian cycle, but also the central nervous system, with effects on neurophysiological parameters such as cognitive performance, attention level and alertness level. The existing positive and negative relationships between light and some diseases such as seasonal depression, Alzheimer’s syndrome, sleep disorders and premature birth are also examined. Furthermore, this chapter provides a general description of the functioning of the human circadian system, the factors that regulate it and its effects on the organism. Finally, it analyses the possible relationships between the circadian cycle and the modern environment, with particular reference to the human interior spaces.
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