Not long ago people got up at sunrise and got to bed at sunset. In the history of evolution, our inner clock got adapted to this everyday bright- and dark-phases and uses these signals for regulation of our sleep- and energy-cycles. This cycle is called circadian rhythm (Latin for: daylong). It also regulates the emotional mood as well as our vital energy. When the sun is shining we are feeling excited and buoyant –- and on the other hand, we are calmer and rather retreat, when it is dark. When our eyes perceive darkness the brain produces night-hormones like melatonin, adenosine and orexin. Since our eyes transfer light into the suprachiasmatic nucleus (SCN) –- our so-called inner clock in our brain (hypothalamus) — this process isn’t only a physiological one.
Light regulates the inner clock of our body which produces active hormones (serotonin) during the day and sleep hormones (melatonin) during the night.
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