Sleep phase

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Sleep phase is the positioning of the subjective night in reference to the clock. Sleep phase is determined by the circadian cycle. In the context of free running sleep or DSPS, it is convenient to represent the sleep phase as the preferred natural waking hour. For example, if one regularly wakes up at 9 am, his sleep phase might be marked as 9:00. See SleepChart: Phase shift graph to see how sleep phase can change in DSPS.

In this book, I try to differentiate between the sleep phase as the end of the subjective night, and the circadian phase as the difference between the time on the clock and the sleep phase.

Warning: Some authors will also confusingly use the term sleep phase to refer to stages of sleep such as REM sleep, Stage 3 sleep, slow wave sleep, etc.

See also:

This glossary entry is used to explain "Good sleep, good learning, good life" (2017) by Piotr Wozniak

Phase shift graph shows the degree of phase-shift as well as its dependence on the time of day and can be used to see the expected bedtime given a specific natural waking time
Phase shift graph shows the degree of phase-shift as well as its dependence on the time of day and can be used to see the expected bedtime given a specific natural waking time

Figure: Phase shift graph shows the degree of phase shift as well as its dependence on the timing of sleep. The graph can be used to see the expected bedtime given a specific natural waking time. Blue line shows the bedtime (vertical axis) for days with a given waking hour (horizontal axis). Red line shows the next day's waking hours (which are shifted by 1-2 hours in DSPS). Fuchsia and gray lines indicate the siesta period. Even though the red waking line begins at the origin of the graph, it shows a substantial phase shift at later hours (DSPS). From the presented exemplary graph one can read that for the waking time equal to 7 am (horizontal axis), the expected time to go to bed, as indicated by the blue line, is 1 am (vertical axis), while optimum siesta time occurs between 15:00 and 16:00. However, if the wake time is 11 am, the bedtime is likely to come only at 5 am the next day