ESSENTIAL Health Considerations on Polyphasic Schedules: The ULTIMATE Course on the Dark Period

The Ultimate Dark Period Course

Important Notes

  • WORK-IN-PROGRESS. Don’t expect the full course by taking it now.
  • If you feel bothered by signing up, you can still view the abbreviated guide right below. 


Have you ever wondered if polyphasic sleeping is healthy? This is a perfectly reasonable question to ask, because you are changing the rhythm of your body so drastically. The ugly truth is that it may not be healthy; this is unless you take the right precautions.
You need to ensure a healthy circadian stability by keeping an intact dark period.

In short, the dark period is when you aren’t exposed to green & blue light. As will be covered in details later, this is possible with red glasses, red lighting or staying in complete darkness.

My name is Crimsonflwr and I am one of the people with the initiative of having a dark period. Back in the early days of the community, it was common practice to use red glasses to block out blue & green light around 1 to 2 hours before the main SWS core. However, literally no one even considered using them after you wake up from the core.

I got the idea for the dark period by making a correlation between plants and lighting conditions. Furthermore,  after researching the topic thoroughly, I came to the conclusion that the whole approach to polyphasic sleeping needed to change to make sure that people stay healthy. Apparently, this does also account for when they change their schedules.

In this course, you will also learn the background for this information & will be able to understand the importance of maintaining a good circadian health.

Discussion Topics

  • The circadian rhythm: what it is, what affects it and why you need to consider it.
  • What the dark period is with general information around it.
  • How to schedule dark periods around polyphasic schedules.
  • What products you can buy to help establish a good dark period.
  • What software you can use to filter out blue and green light from electronical devices.
  • An ultimate beginner-friendly light-filtering calculator that you can use to see if your current light filtering setup qualifies.
  • Issues that come with a dark period and how to overcome them.
  • Finding out how to determine the peak times for sleep by using the three noons.
  • How to stop being a slave to your body and shift the circadian rhythm according to your will.

Dark Period for Beginners

The dark period is one of the most recently discovered utilities for polyphasic sleeping. Needless to say, it is very important. However, since this post only covers the most basic points for beginners, it does not contain all advanced tips. As said earlier, you will be able to fully view all sections by signing up!

Because of the nature of the dark period, it may be intrusive to social evening time as well. For more relevant difficulties, check out the video above about how to handle such obstacles. 

Melatonin Mechanisms

Melatonin is important for proper SWS initiation and healthy sleep architecture1. Note that this is melatonin secretion in the body, not melatonin supplement sources. 

  • An inherent feature of circadian rhythm and melatonin secretion is the suppression and delay of onset following exposure to blue and green light (wavelengths 400-530 nm), by 65-81%2, or roughly 2h3.
  • This feature of the rhythmic processes has been very effective in aiding the entrainment of circadian rhythms with the day-night cycle as blue light was only available during day. However, in recent years, it became increasingly apparent that this can have adverse side effects of circadian misalignment. This effect worsens when combined with exposure to artificial lighting during night time.
  • Some studies suggest that as little as 100 lux of room lights for 6.5 hours4, or 250 lux (office lighting) is enough to completely disrupt the melatonin levels5. These findings warrant minimizing all non-red light types during the dark period. This should not, however, be done in exchange for increasing brightness of red light sources. Red light may have the same effect as light in the blue/green frequencies, but to a lesser extent.
  • Some studies have linked the misalignment of circadian processes with elevated risks of developing cardiovascular diseases6, diabetes7 and cancer8;hence, it is unlikely the impact on sleep is the only possible negative outcome.

Dark Period Setup

  • The dark period should start 2-3h prior to the core. This could be the first core on DC schedules or night core on TC schedules for example.
  • The dark period should continue for 6-12h (preferably 8-10h) after it begins. This period also includes sleeping hours. The reason it should continue even after your wake time, if you have a short core, is to ensure the stability of the circadian rhythm.
  • Light9 and food0 can alter the start of the circadian day.  This in return results in a shift of the SWS and REM peaks accordingly. Darkness is still preferable over red light.
  • One can simply block lights by wearing blue-green light blocking glasses like red colored laser safety goggles. Make sure the glasses block the right wavelengths; many glasses (like yellow-tinted ones) actually allow green light to leak through. Having side protection is also desirable.
  • Using programs such as F.lux and Sunsetscreen on a low Kelvin setting (around 1000K) is also possible if you’re only exposing yourself to light from screens.
  • Using red light bulbs is also an option.

Dark Period on Polyphasic Sleep Schedules

  • Dual Core: If your cores are within 5h from each other, then the dark period should cover the whole core gap.
  • Everyman: If the first nap is relatively close to the core, you should extend the dark period until the nap. Try to have the dark period between 8 and 12 hours long.
  • Tri Core:
  1. For Triphasic, the dark period should cover the wake gap between two cores at night.
  2. For TC1 and TC2, the dark period should cover at least two of the cores. This is according to their sleep placements relative to the local time.
  • For other schedules, a good rule is to follow the day-night cycle of your country. However, if you live in location near the poles, you may want to create an artificial light and dark period to establish a stable cycle over the course of the year. This also protects you from any seasonal affective disorders due to the greatly fluctuating light levels.

Dark Period & Meal Time

Fasting (consuming only water) should coincide with the dark period. Nighttime eating has a strong correlation with an increased risk of some diseases. This include night eating syndrome and sleep-related eating disorder. Furthermore, both of these diseases often result in the following:

  • Increased body mass,
  • obesity,
  • psychiatric disturbances1,
  • diabetes2,
  • delayed sleep onset,
  • worse quality sleep3
  • improperly set the circadian morning.

Aim to have the fast last for at least 8-12 hours34. If it is too hard to curb the hunger, try to minimize the consumption of carbohydrates in the evening. In addition, only consume low caloric foods with low glycemic index (GI) instead. This has anecdotally helped people, mostly because of the slow blood sugar and energy release.

Main author: Crimson

Page last updated: 9 April 2021

Concluding Remark

By taking this course, you will learn essential do’s & dont’s about polyphasic sleep. These will help you stay healthy even when altering your sleep pattern in such a radical way as polyphasic sleep allows! There will also be a lot of videos, pictures, tools & more in this course to help you learn better!

Main author: Crimsonflwr & GeneralNguyen

Course last updated: 9 April 2021


  1. Fourtillan J. Role of melatonin in the induction and maintenance of sleep. Dialogues Clin Neurosci. 2002;4(4):395-401. [PubMed]
  2. Wright H, Lack L. Effect of light wavelength on suppression and phase delay of the melatonin rhythm. Chronobiol Int. 2001;18(5):801-808. [PubMed]
  3. Kayumov L, Casper RF, Hawa RJ, et al. Blocking Low-Wavelength Light Prevents Nocturnal Melatonin Suppression with No Adverse Effect on Performance during Simulated Shift Work. T. 2005;90(5):2755-2761. doi:10.1210/jc.2004-2062. 
  4. Zeitzer J, Dijk D, Kronauer R, Brown E, Czeisler C. Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression. J Physiol. 2000;526(Pt 3):695-702. [PubMed]
  5. Trinder J, Armstrong S, O’Brien C, Luke D, Martin M. Inhibition of melatonin secretion onset by low levels of illumination. J Sleep Res. 1996;5(2):77-82. [PubMed]
  6. Thosar S, Butler M, Shea S. Role of the circadian system in cardiovascular disease. J Clin Invest. 2018;128(6):2157-2167. [PubMed]
  7. Kurose T, Yabe D, Inagaki N. Circadian rhythms and diabetes. J Diabetes Investig. 2011;2(3):176-177. [PubMed]
  8. Fu L, Kettner N. The circadian clock in cancer development and therapy. Prog Mol Biol Transl Sci. 2013;119:221-282. [PubMed]
  9. Crowley S, Eastman C. Phase advancing human circadian rhythms with morning bright light, afternoon melatonin, and gradually shifted sleep: can we reduce morning bright light duration? Sleep Med. 2014;16(2):288-297. [PubMed]
  10. Wehrens S, Christou S, Isherwood C, et al. Meal Timing Regulates the Human Circadian System. Curr Biol. 2017;27(12):1768-1775.e3. [PubMed]
  11. Zawilska J, Santorek-Strumiłło E, Kuna P. [Nighttime eating disorders–clinical symptoms and treatment]. Przegl Lek. 2010;67(7):536-540. [PubMed]
  12. Qin L-Q, Li J, Wang Y, Wang J, Xu J-Y, Kaneko T. The effects of nocturnal life on endocrine circadian patterns in healthy adults. L. 2003;73(19):2467-2475. doi:10.1016/s0024-3205(03)00628-3. [PubMed]
  13. Crispim C, Zimberg I, dos R, Diniz R, Tufik S, de M. Relationship between Food Intake and Sleep Pattern in Healthy Individuals. J Clin Sleep Med. 2011;7(6):659-664. [PubMed]
  14. Longo V, Panda S. Fasting, circadian rhythms, and time restricted feeding in healthy lifespan. Cell Metab. 2016;23(6):1048-1059. [PubMed]



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