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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 (2h is recommended in most cases) 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 == <!--T:2-->
== Rationale == <!--T:2-->
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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|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.
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|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 == <!--T:6-->
== Timing == <!--T:6-->
* For [[Special:MyLanguage/E2|E2]], [[Special:MyLanguage/E3|E3]] (including extended), and [[Special:MyLanguage/E4|E4]] it should last until the end of first nap as long as that nap is within 5 hours of the core.
* For [[Special:MyLanguage/E2|E2]], [[Special:MyLanguage/E3|E3]] (including extended), and [[Special:MyLanguage/E4|E4]] it should last until the end of first nap as long as that nap is within 5 hours of the core.
* For [[Special:MyLanguage/Segmented|Segmented]] and [[Special:MyLanguage/Dual core|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 [[Special:MyLanguage/Segmented|Segmented]] and [[Special:MyLanguage/Dual core|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 == <!--T:9-->
== Mechanism == <!--T:9-->
[[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> 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.
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 == <!--T:11-->
== Methods == <!--T:11-->
=== Goggles === <!--T:12-->
=== Goggles === <!--T:12-->
* The light red goggles let in substantially more red and green light than the orange one, but less yellow. The overall brightness appears to be slightly higher for the orange one, but the orange one allows for more colour perception. Based on the melanopic sensitivity function, both should provide similar levels of protection against melatonin suppression.
* The light red goggles let in substantially more red and green light than the orange one, but less yellow. The overall brightness appears to be slightly higher for the orange one, but the orange one allows for more colour perception. Based on the melanopic sensitivity function, both should provide similar levels of protection against melatonin suppression.
* There is a significant price difference between the first two and the third and the fourth one. However, the third and fourth ones have better quality (fewer rough edges on the plastic, more uniform transparency, and provide more options).
* There is a significant price difference between the first two and the third and the fourth one. However, the third and fourth ones have better quality (fewer rough edges on the plastic, more uniform transparency, and provide more options).
=== Red interior lighting === <!--T:14-->
=== Red interior lighting === <!--T:14-->
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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.
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 === <!--T:16-->
=== Computer screen colour filters === <!--T:16-->
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'''Note''' that, even with all the red colour filtered away, all screens, with the exception of OLED screens on some phones, '''will bleed backlight''', which is white and can compromise your dark period. Depending on the quality and brightness setting of your screen, this may or may not be an issue.
'''Note''' that, even with all the red colour filtered away, all screens, with the exception of OLED screens on some phones, '''will bleed backlight''', which is white and can compromise your dark period. Depending on the quality and brightness setting of your screen, this may or may not be an issue.
== Living with dark period == <!--T:20-->
== Living with dark period == <!--T:20-->
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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.
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 === <!--T:22-->
=== Monochromatic filters === <!--T:22-->
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On Windows 10, you can use the key combination Ctrl + Windows + C to toggle a grayscale filter. This can be configured by finding Turn color filters on or off from the start menu.
On Windows 10, you can use the key combination Ctrl + Windows + C to toggle a grayscale filter. This can be configured by finding Turn color filters on or off from the start menu.
=== Colour pickers === <!--T:28-->
=== Colour pickers === <!--T:28-->
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When there is a need to determine some colours with precision, it is best to use a colour picker program. These programs grabs a pixel from your screen and records the brightness value in each of the subpixels.
When there is a need to determine some colours with precision, it is best to use a colour picker program. These programs grabs a pixel from your screen and records the brightness value in each of the subpixels.
=== Prescription glasses === <!--T:30-->
=== Prescription glasses === <!--T:30-->
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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.
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 ==== <!--T:36-->
==== Glue lenses onto the goggles ==== <!--T:36-->
* 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.
* 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 will not be easy to remove once attempted.
* The glue will not be easy to remove once attempted.
== Related advice == <!--T:40-->
== Related advice == <!--T:40-->
=== Fasting period === <!--T:41-->
=== Fasting period === <!--T:41-->
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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.
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 === <!--T:43-->
=== Exercise === <!--T:43-->
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Intense exercise such as strenuous weight lifting and long-distance running should be avoided during dark period, as this 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.
Intense exercise such as strenuous weight lifting and long-distance running should be avoided during dark period, as this 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 == <!--T:45-->
== See also == <!--T:45-->
* [[Special:MyLanguage/Crimsonflwr|Crimsonflwr]]'s free and comprehensive dark period [https://www.polyphasic.net/courses/dark-period-course/ course] (registration to polyphasic.net required).
* [[Special:MyLanguage/Crimsonflwr|Crimsonflwr]]'s free and comprehensive dark period [https://www.polyphasic.net/courses/dark-period-course/ course] (registration to polyphasic.net required).
* [[Special:MyLanguage/Crimsonflwr|Crimsonflwr]]'s dark period [https://docs.google.com/spreadsheets/d/10dAiiTWo4V6Fq2P0b4_xjSyvdydOHcz68BLxWGyFlSw/edit?usp=sharing calculator]. Refer to the above course for instructions regarding usage.
* [[Special:MyLanguage/Crimsonflwr|Crimsonflwr]]'s dark period [https://docs.google.com/spreadsheets/d/10dAiiTWo4V6Fq2P0b4_xjSyvdydOHcz68BLxWGyFlSw/edit?usp=sharing calculator]. Refer to the above course for instructions regarding usage.
== References == <!--T:47-->
== References == <!--T:47-->
