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Dark period is a way for sleepers to stabilize their circadian rhythms in the absence of long blocks of sleep and increase the quality of SWS. For most schedules, it should start 1.5-3 hours before the dusk (SWS peak) sleep block and continue for around 8 to 12 hours afterwards.
Dark period is a way for sleepers to stabilize their circadian rhythms in the absence of long blocks of sleep and increase the quality of [[Wikipedia:Slow-wave sleep|SWS]]. For most schedules, it should start 1-3 hours before the dusk (SWS peak) sleep block and continue for around 8 to 12 hours afterwards.
== Rationale ==
== Rationale ==
Modern humans often use electric lighting during the night. This can cause difficulty sleeping, as the body thinks it is still daytime even if it is already midnight, and is the reason why people often experience the desire to sleep later and later each day. For monophasic sleepers, a somewhat short dark period can be maintained during their sleep hours, which keeps their circadian rhythms relatively stable.
Modern humans often use electric lighting during the night. This can cause difficulty sleeping, as the body thinks it is still daytime even if it is already midnight, and is the reason why people often experience the desire to sleep later and later each day. For monophasic sleepers, a somewhat short dark period can be maintained during their sleep hours, which keeps their circadian rhythms relatively stable.
However, for polyphasic sleepers who might not have such long sleep blocks, this poses an issue. As artificial light is present around the clock, melatonin production is suppressed and the quality of SWS is compromised. This causes extra difficulty in adaptation and is also unhealthy. To avoid this, polyphasic sleepers (and monophasic sleepers too, for extra benefits) should practice a dark period, during which no blue and green light should enter the eye.
However, for polyphasic sleepers who might not have such long sleep blocks, this poses an issue. As artificial light is present around the clock, [[Wikipedia:melatonin]] production is suppressed and the quality of SWS is compromised. This causes extra difficulty in adaptation and is also unhealthy, as circadian disruption is linked to various health issues.<ref>https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4632990/</ref> To avoid this, polyphasic sleepers (and monophasic sleepers too, for extra benefits) should practice a dark period, during which no blue and green light should enter the eye.
== Timing ==
The optimal timing of dark period depends on your schedule. For most schedules, it should begin around 1-3 hours (the default recommendation is 2 hours) before your '''dusk/evening''' sleep (core for [[Everyman]], first core for [[Dual core]], [[TC1]], and [[TC2]], and evening core for [[Triphasic]].
For [[E1]] and [[Siesta]], it should start before core and end immediately upon waking.
For [[E2]], [[E3]] (including extended), and [[E4]] it should last until the end of first nap.
For [[Segmented]] and [[Dual core]], it should cover the entire core gap (gap between first and second core for Tri core), so long as it does not exceed 12 hours.
== Mechanism ==
== Mechanism ==
