Changes

<!--T:4-->

<!--T:4-->

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.<ref>Eun Yeon Joo, Sabra M Abbott, Kathryn J Reid, Donghong Wu, Joseph Kang, John Wilson, Phyllis C Zee (April 2017). ''[https://www.sciencedirect.com/science/article/abs/pii/S1389945716302295 Timing of light exposure and activity in adults with delayed sleep-wake phase disorder]''. Sleep Medicine, Volume 32, April 2017, Pages 259-265, https://doi.org/10.1016/j.sleep.2016.09.009</ref> For monophasic sleepers, a somewhat short dark period can be maintained during their long 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.<ref name="Joo2017" /> For monophasic sleepers, a somewhat short dark period can be maintained during their long sleep hours, which keeps their circadian rhythms relatively stable.

<!--T:5-->

<!--T:5-->

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 name="pmid25635592" /> 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-->

<!--T:10-->

<!--T:10-->

[[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 name="cie15" /> 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-->

<!--T:13-->

<!--T:13-->

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 [[Special:MyLanguage/Polyphasic Sleep Discord|Discord community]]). There are several types of these available, and below is a comparison between their light-filtering lens tints:

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 [[Special:MyLanguage/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)

|[[File:Light red goggles.png|frameless|253x253px]]

|[[File:Light red goggles.png|frameless|253x253px]]

|-

|-

|Orange

|Orange 2

[https://aliexpi.com/zCJv aliexpress]

[https://www.amazon.com/dp/B07DC6D11R amazon]

|[[File:Orange goggles 2.jpg|frameless]]

[https://www.ebay.com/itm/143801500303 ebay]

[https://www.ebay.com/itm/143801500303 ebay]

|[[File:Orange goggles profile.png|frameless|238x238px]]

|[[File:Orange goggles profile.png|frameless|238x238px]]

|Recommended

|Recommended

|[[File:Orange goggles.png|frameless]]

|[[File:Orange goggles.png|frameless]]

|-

|-

|Yellow

|Yellow

|[[File:Yellow goggle profile.png|frameless|241x241px]]

|[[File:Yellow goggle profile.png|frameless|241x241px]]

|50%

|50%

|Acceptable

|Useful but not ideal

|[[File:Yellow goggles.png|frameless]]

|[[File:Yellow goggles.png|frameless]]

|-

|-

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 color filters === <!--T:16-->

<!--T:17-->

<!--T:17-->

{| class="wikitable"

{| class="wikitable"

|+Comparison of colour filter software

|+Comparison of color filter software

!Name

!Name

!OS support

!OS support

|Windows

|Windows

|Yes

|Yes

|[https://www.neowin.net/news/sunsetscreen-128/ last freeware version]

|[https://www.neowin.net/news/sunsetscreen-128/ last full free version]

|[https://justgetflux.com/faq.html faq link]

|-

|-

|Redshift

|Redshift

|Yes

|Yes

|[https://wiki.archlinux.org/index.php/redshift#Configuration configuration last full free version]

|[https://wiki.archlinux.org/index.php/redshift#Configuration configuration last full free version]

|-

|-

|iOS&macOS native feature

|iOS&macOS native feature

|No

|No

|[https://www.skyatnightmagazine.com/advice/how-to-turn-your-iphone-screen-red-for-astronomy/ tutorial]

|[https://www.skyatnightmagazine.com/advice/how-to-turn-your-iphone-screen-red-for-astronomy/ tutorial]

|}

|}

For all of these software packages, you should change the colour temperature to the minimum possible (1000K for redshift, 1200K for f.lux).

For all of these software packages, you should change the color temperature to the lowest possible usable value (1000K for redshift, 800K for f.lux).

 

 

It offers 12 different predefined color modification schemes, which tend to produce more usable and vastly more customizable results (it is possible to create custom inversion profiles with the help of a GUI application) than the more basic color inversion software like the integrated Windows color inversion mode. Of particular interest for the purpose of DP management is the "'''inverted red'''" mode, which drastically reduces the amount of visible light emitted by the display (especially when originally light colored content was presented on the screen), while having a similar color shifting effect to the other software presented above.

<!--T:18-->

<!--T:18-->

For Linux on Wayland, please use the night light options offered by your desktop environment (KDE and GNOME offer this feature). Editing the colour temperature manually might be necessary to achieve the amount needed. [https://www.omgubuntu.co.uk/2017/07/adjust-color-temperature-gnome-night-light Change colour temperature on GNOME]

For Linux on Wayland, please use the night light options offered by your desktop environment (KDE and GNOME offer this feature). Editing the color temperature manually might be necessary to achieve the amount needed. [https://www.omgubuntu.co.uk/2017/07/adjust-color-temperature-gnome-night-light Change color temperature on GNOME]

<!--T:19-->

<!--T:19-->

'''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 color filtered away, all screens, except for 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-->

<!--T:44-->

<!--T:44-->

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 name="Wolff2019" /> 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-->

<!--T:48-->

<!--T:48-->

<references />

<ref name="Wolff2019">{{cite journal |vauthors=Wolff CA, Esser KA |date=2019 |title=Exercise timing and circadian rhythms |journal=Current Opinion in Physiology |volume=10 |pages=64-69 |doi=10.1016/j.cophys.2019.04.020 |issn=2468-8673}}</ref>

<!--T:49-->

<!--T:49-->