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f.luxometer rating

Your body has a non-linear "dose-response" to light. This graph shows you how light of various intensities translate to a shift in your circadian timing.

When you see light in the morning, it makes your day shorter, and when you see bright light at night, you stay up later.

"Phase shift" shows how much you can move your body clock in just one night if you see it for long enough (a few hours) at the right time of day, typically before bed. Also, you can see how the light compares to being outdoors on a sunny day, which can shift your body's internal clock by up to 3 hours. This is how your body adjusts its clock when traveling to another timezone.

To find this number, we're using a best fit from several published studies, with subjects who viewed light exposures ranging from 90 minutes to 6 hours.