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[[File:Melanopic.jpg|thumb|Melanopic sensitivity function]]
[[File:Melanopic.jpg|thumb|Melanopic sensitivity function]]
In modern times with the advent of artificial light, many people's circadian rhythms have been pushed forward (i.e. later). However, this exposure to artificial light sources also compromises people's ability to gain SWS efficiently. The extent to which light influences the circadian rhythm is given by the melanopic sensitivity function, which peaks at ~480nm (blue) and drops off on both sides. To reduce this effect, a [[dark period]] must be employed, during which blue and green lights must not enter the eye. This can be done in many ways, such as with [[red goggles]] or [[screen filters]].
In modern times with the advent of artificial light, many people's circadian rhythms have been pushed forward (i.e. later). However, this exposure to artificial light sources also compromises people's ability to gain SWS efficiently. The extent to which light influences the circadian rhythm is given by the melanopic sensitivity function, which peaks at ~480nm (blue) and drops off on both sides. To reduce this effect, a [[dark period]] must be employed, during which blue and green lights must not enter the eye. This can be done in many ways, such as with [[red goggles]] or [[screen filters]].
To maintain the stability of the circadian rhythm, all polyphasic sleep schedules must stay relatively consistent day-to-day, without large changes in core or dark-period timings. As such, schedules that are not aligned with the 24-hour day are unsustainable and unhealthy.
==Minimum sleep threshold==
==Minimum sleep threshold==
Siesta-ext, Segmented-ext
Siesta-ext, Segmented-ext
|7-8
|7-8
|Negligible
|<1 hour
|
|
|-
|-
==Sleep block lengths==
==Sleep block lengths==
Sleeps on polyphasic schedules are broadly characterized as [[cores]] and [[naps]].
Cores are long blocks of sleep that contain at least one full sleep cycle. They are typically scheduled to be a multiple of a 90 minutes, which is a common sleep cycle length. However, alternative core lengths can be done to either to plan for alternative cycle lengths or in an effort to gain extra time in SWS or REM. Cores are generally considered to be essential, because they provide the necessary amount of SWS to sustain life. As such, schedules without cores (i.e. [[Nap only|nap only schedules]]) have extremely low success rates.
Naps are short blocks of sleep, typically about 20 minutes on default schedules. Naps allow for a small amount of REM to be gained. Moreover, naps help sleepers sustain wakefulness through gaps. Longer up to (~45 minute) naps can be used in during the REM peak around dawn to gain even more time in REM. Longer naps in other times of the day can lead to SWS wakes, which can be exceptionally difficult to wake from for some people, especially during periods of high SWS deficit.
Core sleeps are favoured during night time, as they allow sufficient time to complete SWS-filled sleep cycles. They are also easier to schedule at night for most people due to social obligations. Naps are favoured in the day, since deeper sleep stages are less likely to appear then. After adaptation, naps can be relatively flexible, whereas cores are much harder to move.
==Consistency==
==Consistency==
