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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 [[Wikipedia:Slow-wave sleep|SWS]]. It also prevents certain health issues from arising. 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.
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]]. It also prevents certain health issues from arising. For most schedules, it should start 1-3 hours (2h is recommended in most cases) before the dusk (SWS peak) sleep block and continue for around 8 to 12 hours afterwards.
== Rationale ==
== Rationale ==
Before the advent of electrical lighting in modern times, humans historically had a stable time during the night in which there is little light. This helped stabilize their circadian rhythms and kept them synced to the natural day/night cycle.
Before the advent of electrical lighting in modern times, humans historically had a stable period of time during the night in which there was little light. This kept their circadian rhythms stable and synchronized to the natural day/night cycle.
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 as the body thinks it is still daytime even if it is already midnight, and is part of 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 long 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, [[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.
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) should practice a dark period, during which no blue, green or white (as this contains both blue and green) light should enter the eye.
== Timing ==
== Timing ==
* For [[E1]] and [[Siesta]], it should start before core and end immediately upon waking.
* 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 [[E2]], [[E3]] (including extended), and [[E4]] it should last until the end of first nap as long as that nap is within 5 hours of the core.
* 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.
* 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 ==
[[File:Melanopic.png|thumb]]
[[File:Melanopic.png|thumb]]
The intrinsically photosensitive retinal ganglion cells (ipRGCs) controls the secretion of melatonin by the pineal gland. Their sensitivity to light is independent from normal vision, which is mediated by cones and rods in the eyes. The ipRGCs have a peak sensitivity at 480 nm and drops off on both sides.<ref>CIE TN 003:2015, Report on the First International Workshop on Circadian and Neurophysiological Photometry, 2013, published 2015</ref> Based on this, in order to avoid melatonin suppression, only yellow-orange and red light should be allowed during the dark period.
The intrinsically photosensitive retinal ganglion cells (ipRGCs) controls the secretion of melatonin by the pineal gland. Their sensitivity to light is independent from normal vision, which is mediated by cones and rods in the eyes. The ipRGCs have a peak sensitivity at 480 nm and drops off on both sides.<ref>CIE TN 003:2015, Report on the First International Workshop on Circadian and Neurophysiological Photometry, 2013, published 2015</ref> During the dark period it is preferable to avoid light altogether, as all light provides some melatonin suppression, but this is not reasonable for most people's lifestyles. Instead, is best to simply avoid as much bright light as possible, and limit light intake to only necessary yellow, orange and red light in order to limit melatonin suppression as much as possible.
== Methods ==
== Methods ==
=== Goggles ===
=== Goggles ===
The most popular and versatile method for achieving a dark period is through the use of red-coloured laser goggles (colloquially known as "DP goggles" in the [[Polyphasic Sleep Discord|Discord community]]). There are several types of these available, and below is a comparison between them:
The most popular and versatile method for achieving a dark period is through the use of red-coloured laser goggles (colloquially known as "DP goggles" in the [[Polyphasic Sleep Discord|Discord community]]). There are several types of these available, and below is a comparison between their light-filtering lens tints:
{| class="wikitable"
{| class="wikitable"
|+Comparison of commonly available red goggles (links not sponsored)
|+Comparison of commonly available red goggles (links not sponsored)
=== Red interior lighting ===
=== Red interior lighting ===
If you live in your own room, it is possible to use either RGB or pure red LED lights during dark period to avoid the inconvenience and/or discomfort from wearing goggles.
If you live in a space where you are in control of the lighting, it is possible to use either RGB or pure red LED lights during dark period to avoid the inconvenience and/or discomfort from wearing goggles. However, you must still be sure that you wear dark period glasses when looking at screens such as your electronic devices, and if you live in an area with bright lights outside your house, it is best to draw your blinds (blackout curtains ideally) in order to block any external light.
=== Computer screen colour filters ===
=== Computer screen colour filters ===
== Living with dark period ==
== Living with dark period ==
Using any of the above methods to achieve a dark period would virtually remove your ability to see all non-red lights. This can impair you ability to do work. However, there are some methods to mitigate this.
Using any of the above methods to achieve a dark period should limit the accuracy of your perception of non-red lights during your dark period. This may impair you ability to do certain tasks. However, there are some methods to mitigate this.
=== Monochromatic filters ===
=== Monochromatic filters ===
=== Prescription glasses ===
=== Prescription glasses ===
If you need prescription glasses for vision correction, you need to wear both at the same time.
If you need prescription glasses for vision correction, you may wear both at the same time via any of the three methods listed below.
==== Wear them outside the goggles ====
==== Wear them outside the goggles ====
Wearing your prescription glasses outside the goggles is the preferred option for the first and second goggle types on the table, as there is less light leakage.
==== Wear them inside the goggles ====
==== Wear them inside the goggles ====
It may be possible to wear most styles of corrective lenses inside of dark period goggles, depending on the model of your goggles. The orange and yellow goggles as pictured in the above table can fit over many glasses models, but it may not be particularly comfortable, depending on the shape of the prescription frames.
==== Glue lenses onto the goggles ====
==== Glue lenses onto the goggles ====
This might be the most comfortable option once completed. Obtain your lenses by detaching them from the glasses, and glue them to the top of your goggles. Hot glue will not melt either the lenses or the first two goggles (the others have not been confirmed).
This might be the most comfortable option once completed. Detaching your prescription lenses from their frames and glue them to the top of your goggles. Hot glue will not melt either the lenses or the first two goggles (the others have not been confirmed).
[[File:Lenses on goggles.jpg|thumb|Example]]
[[File:Lenses on goggles.jpg|thumb|Example]]
* Choose the glasses that match in curvature with your goggles, so it would be easier to attach.
* Choose the glasses that match in curvature with your goggles, so it would be easier to attach.
* Seal the gap completely around to prevent moisture from getting in, as it will be extremely difficult to remove afterwards.
* Seal the gap completely around to prevent moisture from getting in, as it will be extremely difficult to remove afterwards.
* Perform the operation in a dry, and preferable cold environment to minimize the amount of moisture in the gap. Failure to do so can result in the goggles fogging up in cold environments.
* Perform the operation in a dry and preferable cold environment to minimize the amount of moisture in the gap. Failure to do so can result in the goggles fogging up in cold environments.
Warnings:
Warnings:
* Might cause slight dizziness at first due to axial misalignment.
* Might cause slight dizziness at first due to axial misalignment. Try holding your prescription lenses in front of and behind your dark period goggles while they're on your face to determine which feels better before gluing them.
* The glue would not be easy to remove once attempted.
* The glue will not be easy to remove once attempted.
== Related advice ==
== Related advice ==
=== Fasting period ===
=== Fasting period ===
It is recommended that you maintain a fasting period that covers the entirety of your dark period, as food is also an important [[Wikipedia:zeitgeber|zeitgeber]], or circadian cue. Intermittent fasting has been anecdotally suggested to work well with polyphasic sleep. It is preferable to eat during the day rather than at night. A breakfast helps set the circadian day start.
It is recommended that you maintain a fasting period that covers the entirety of your dark period, as food is also an important [[Wikipedia:zeitgeber|zeitgeber]], or circadian cue. Intermittent fasting has been anecdotally suggested to work well with polyphasic sleep. It is preferable to eat during the day rather than at night. A breakfast helps set the circadian day start. Water may be consumed, but any xenobiotic consumables will disrupt your circadian rhythm.
=== Exercise ===
=== Exercise ===
Intense exercise such as lifting and long-distance running should be avoided during dark period, as they might disrupt the circadian rhythm.<ref>Christopher A Wolff, Karyn A Esser, Exercise timing and circadian rhythms, Current Opinion in Physiology, Volume 10, 2019, Pages 64-69, ISSN 2468-8673, <nowiki>https://doi.org/10.1016/j.cophys.2019.04.020</nowiki>.</ref> In addition, exercise may also disrupt sleep, which is usually in close proximity during dark period. However, during adaptation, it might be desirable to use exercise as a means to stay awake. Choose mild exercise routines and do not exercise for an extended period for this purpose.
Intense exercise such as strenuous weight lifting and long-distance running should be avoided during dark period, as they might disrupt the circadian rhythm.<ref>Christopher A Wolff, Karyn A Esser, Exercise timing and circadian rhythms, Current Opinion in Physiology, Volume 10, 2019, Pages 64-69, ISSN 2468-8673, <nowiki>https://doi.org/10.1016/j.cophys.2019.04.020</nowiki>.</ref> In addition, exercise may also disrupt sleep and/or increase sleep onset as a result of increased heart rate. However, during adaptation, it might be desirable to use exercise as a means to stay awake. Choose mild exercise routines and do not exercise for an extended period of time to avoid circadian disruption or sleep onset issues; both of which may hinder your sleep quality and harm your adaptation.
== See also ==
== See also ==
* [[Crimsonflwr]]'s dark period [https://www.polyphasic.net/courses/dark-period-course/ course] (registration required)
* [[Crimsonflwr]]'s free and comprehensive dark period [https://www.polyphasic.net/courses/dark-period-course/ course] (registration to polyphasic.net required).
* [[Crimsonflwr]]'s dark period [https://docs.google.com/spreadsheets/d/10dAiiTWo4V6Fq2P0b4_xjSyvdydOHcz68BLxWGyFlSw/edit?usp=sharing calculator]. Refer to the above course for instructions.
* [[Crimsonflwr]]'s dark period [https://docs.google.com/spreadsheets/d/10dAiiTWo4V6Fq2P0b4_xjSyvdydOHcz68BLxWGyFlSw/edit?usp=sharing calculator]. Refer to the above course for instructions regarding useage.
== References ==
== References ==
