We rely on sunlight and the lack of it to ‘tell’ our bodies when it’s time for wakefulness and for sleep. It’s responsible for our circadian rhythm, which is essentially a 24 hour wake/sleep pattern of our biological functions. The 24 hour cycle of sunlight and darkness keeps everyone’s ‘internal’ clocks synchronized in a particular geographic location. If you fly to another part of the world, your circadian rhythm eventually adjusts to the day/night cycle of the particular locality. It turns out that the blue-green part of sunlight is responsible.

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