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Dark period is a way for sleepers to stabilise their circadian rhythms in the absence of long blocks of sleep. 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 stabilise 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.
== Rationale ==
== Rationale ==
== 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. 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> Based on this, in order to avoid melatonin suppression, only yellow-orange and red light should be allowed during the dark period.
== 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]]).
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:
{| class="wikitable"
|+Comparison of commonly available red goggles (links not sponsored)
!Model number
!Absorption profile
!Common name
!Verdict
!Image
|-
|
|
|Light red googles
|Recommended
|
|-
|
|
|Dark red goggles
|Recommended
|
|-
|
|
|Orange goggles
|Recommended
|
|-
|
|
|Yellow goggles
|Avoid unless no alternatives
|
|}
=== Red interior lighting ===
=== Red interior lighting ===
=== Computer screen colour filters ===
=== Computer screen colour filters ===
{| class="wikitable"
|+Comparison of colour filter software
!Name
!OS support
!Automated?
!
|-
|Redshift
|Linux
|Yes
|
|-
|F.lux
|Windows, Linux
|Yes
|
|-
|iOS&macOS native feature
|iOS, macOS
|No
|
|}
== 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.
=== Monochromatic filters ===
Using red goggles or red filters can make it difficult to see certain colors on your screen. To solve this problem, you may wish to temporarily remove colors on your screen with a monochrome/greyscale filter. Here are some ways to do it:
On iOS and macOS, go to Accessibility > Display > Color Filters, turn on Color Filters and select “Greyscale”
On Android, open up Settings, then tap Digital Wellbeing & parental control, then choose Wind Down, you can set up a schedule for the evening, which will turn your screen greyscale for the scheduled time. Alternatively, go to Settings > Developer Options > Simulate colour space and choose Monochromacy. (For this, you need to have Developer Options enabled. Here's how)
On GNOME, you can use the extension Desaturate All to turn your display monochrome with the click of a button.
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.
=== Code editor colourschemes ===
=== Colour pickers ===
== Related advice ==
=== 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.
=== 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.
