Circadian phase
Circadian phase is where your internal clock currently sits relative to the outside cycle of day and night.
What does Circadian phase mean?
Phase is a position on a cycle. The body clock runs on a cycle of about 24 hours, so its phase is where in that cycle you currently are, which is a different question from what time it is or how rested you feel. Researchers pin phase to a physiological marker rather than to a feeling, usually the evening rise in melatonin or the low point in core body temperature, which is why two people sitting in the same room at the same hour can be at different phases. The same light can be an early-morning signal for one of them and a middle-of-the-night signal for the other. Light is the strongest input that moves phase, and the direction depends on when it lands: light after the body-temperature low point, roughly two hours before a person's usual wake time, pulls phase earlier, and light before that point pushes it later. That relationship is called a phase-response curve. It maps alignment, not sleep quality.
Sources cited for Circadian phase
Every number on this Circadian phase page traces to one of the 1 sources below: 1 peer-reviewed.
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