Morning Light & Circadian Timing

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Eyes · Myopia · Screens
Outdoor daylight does two jobs at once. In a randomized trial, schoolchildren given an extra 40 minutes outdoors a day developed less new myopia over three years. The same light also sets the body clock through a class of light-sensing cells in the retina (ipRGCs). Sending a child outside gets both benefits.

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Light is a clock signal

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The most important job of morning light is not to give you energy; it is to set the master clock in your brain — to tell it it is daytime now, and the day starts counting from here. Once the clock is set, it can bring body temperature, cortisol, melatonin, appetite and attention to the right state at the right hours.

This is how the light gets in: in the retina at the back of the eye there is a class of cells that sense light but do not form images (intrinsically photosensitive retinal ganglion cells, ipRGCs). When they catch light, they send an it is light now signal deep into the brain, to the master clock (the suprachiasmatic nucleus, ), which then broadcasts it to the whole body.

That explains why someone can sleep 7 hours and still wake up feeling jet-lagged: the problem is not only that the sleep was too short, but that it landed in a stretch of time the body does not accept as night.

Educational content, not medical advice — consult a clinician.

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Morning Light & Circadian Timing

Story

Connected to · 1

synergy · 1

Eyes · Myopia · Screens
Outdoor daylight does two jobs at once. In a randomized trial, schoolchildren given an extra 40 minutes outdoors a day developed less new myopia over three years. The same light also sets the body clock through a class of light-sensing cells in the retina (ipRGCs). Sending a child outside gets both benefits.

Read full story

Stop 1/5

Light is a clock signal

EVIDENCEREVIEW 1 · MECH 1

READ THE ORIGINAL

The most important job of morning light is not to give you energy; it is to set the master clock in your brain — to tell it it is daytime now, and the day starts counting from here. Once the clock is set, it can bring body temperature, cortisol, melatonin, appetite and attention to the right state at the right hours.

This is how the light gets in: in the retina at the back of the eye there is a class of cells that sense light but do not form images (intrinsically photosensitive retinal ganglion cells, ipRGCs). When they catch light, they send an it is light now signal deep into the brain, to the master clock (the suprachiasmatic nucleus, ), which then broadcasts it to the whole body.

That explains why someone can sleep 7 hours and still wake up feeling jet-lagged: the problem is not only that the sleep was too short, but that it landed in a stretch of time the body does not accept as night.

Educational content, not medical advice — consult a clinician.