this world, you wake up at dawn. Soon, the sun is high in the sky, producing lots of light. This light signals the SCN and we feel awake. In the evening, the light gets dimmer as the sun sinks down towards the horizon. This, along with the time that has passed since you first saw the bright light, signals the SCN to release a hormone called melatonin, making you feel sleepy. But there is another element to this process: the colour of the light. Morning light has a large blue component,3 and blue light, with its short wavelength, is particularly good at resetting the circadian rhythm by
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