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

The Dark Period

The Dark Period: Basics


In this lesson, you will learn to answer the following questions:

  1. What is a dark period?
  2. How long should it be?
  3. What should I avoid doing during the dark period?

The Dark Period

What is the dark period?

Basically, it is the time when you do not expose yourself to light. For most monophasic sleepers, it is when they sleep. Before the introduction of artificial lighting, the dark period would go from sunset to sunrise. However, today we use electronics, so the dark period for the most part artificially shortens in length.

On the other hand, the daytime hours when the sun is up and people are exposing themselves to light is the photoperiod. Thus, the night is the dark period and the day is the photoperiod.

But why are we talking about dark periods?

  • When you are sleeping polyphasically, you have the opportunity to break your dark period even earlier than when you are sleeping monophasically. This is primarily because you have shorter sleep blocks.
  • For example, if you were on a segmented schedule with two 3.5-hour cores, you COULD introduce artificial lighting between the cores. As a result, you only have a 3.5-hour dark period. This is bad, and we will explain it later on. 
  • The main purpose of keeping an artificial dark period is to ensure a good hormonal health with the secondary benefits of improving sleep quality.

Other utilities

Some people have reported needing less sleep when they use a dark period on monophasic sleep. But again, improved sleep is only the secondary benefit. Having a good hormonal health is key because it can permanently affect your health with prolonged messed-up circadian rhythm. Unfortunately, this benefit is mostly invisible, so it does not serve as the best goal to strive for since a good hormonal health should be the norm for most people.

  • That said, a dark period can reduce sleep inertia in the morning.
  • Additionally, it also improves the amount of SWS and REM sleep that you get on polyphasic sleep schedules.

This means that there are clear benefits available for using the dark period, even if the long-term health effects are not in the equation.
Regardless, if you wish to stay adapted to a polyphasic schedule for a long time, you should keep a dark period on the new schedule even after adaptation.

Comparison with plants

Clearly, people are designed to have one uninterrupted block of darkness with light. To illustrate this, humans can be compared to plants.
If you own plants that are not supposed to survive the winter in your country, you know that they will visibly suffer with too much light exposure.

However, if you expose the plants to too little light, they will drop their leaves and become very “sad“. This is very similar to humans, though of course it is not exactly the same. We are not capable of photosynthesis, so this is only a rough comparison.

Excessive light exposure will also disrupt our circadian rhythm. This can lead to several negative effects as in the previous lesson. When you are exposing yourself to too little light, you may become very sad. We will go over this in more detail below.

Dark period scheduling: A general introduction

How long should the dark period be? We have some ideas that can help us with determining its optimal length.

First, I want to point out that an artificial dark period has not seen its use on polyphasic schedules for more than around 2 years. Thus, we do not have exclusive evidence that the lengths I am going to discuss are optimal by any means. We are still investigating to figure out the best dark period duration.

However, the facts are the other way around. We do not know the effects of not having a dark period. Still, we have some ideas for the optimal length of the dark period. Let’s start with the obvious one: dark period duration for monophasic sleepers.

  • Most monophasic sleepers use their phones until minutes before sleeping,  then immediately wake up with bright lights on.
    Nevertheless, you might not know that it is a common cause of insomnia symptoms. This can be alleviated by blocking out light a bit before falling asleep.
  • An optimal monophasic sleepers dark period should be between 8 and 10 hours long.

This is also the number I suggest most people follow; we know monophasic sleepers are safe with their current photoperiod duration.

Next, I want to discuss two of the extremes here:

  • The maximum suggested length of the dark period
  • The minimum suggested length for the dark period.

The maximum duration

The maximum length of the dark period does not really have any conclusive determination, because there really doesn’t seem to be one.
We are talking about the physical damage as a possible result of extended dark periods.
But not using enough light can definitely affect people’s mental health.

  • See, in the northern regions of the world, it is really common that people develop SAD, or Seasonal Affective Disorder during the winter. This leads to similar symptoms as depression. You really want to avoid it because it will significantly damage your productivity.
  • Because of this, it makes sense to limit the dark period to some extent to prevent the development of SAD.

The community recommendation is to not have the dark period be longer than 12 hours for this reason. This threshold is of course individualistic; it might also change depending on the light intensity you expose yourself to during your photoperiod. Thus, if you spend a lot of time outdoors, you might be able to have a longer dark period and still not develop SAD.

The minimum duration

Most people have far more interest in minimizing the dark period because it is harder to stay awake during this period.
In addition, it limits what people can do during this time. But again, the community recommendation is to use a dark period between 8 and 10 hours in length when possible. You should know that going below this number is going to increase the risk of harming your body.

So, the minimum length of the dark period derives from people with a sleep-reduction mutation that allows them 6 hours of daily sleep total while not experiencing any bad effects.

  • This is a mutation to the DEC2 allele. Unlike mutations that cause people to sleep even less than that, it is one of the mutations that do not really have any associated negative side effects.
  • Other mutations that cause people to sleep less than 6 hours can, however, disrupt their circadian rhythms. This is possible because they use shorter dark periods.

So the minimum length of the dark period is about 6 hours long. This is because it is the dark period length that most people with a reduced sleep needs are able to sustain without developing negative effects. However, it is uncertain if this only affects the people with the mutation or if it is a global phenomena. Be sure to proceed with caution.

Securing the structure of the dark period

How do you actually make sure that you are in the dark period even when awake?

  • Basically, minimize the impact of zeitgebers on yourself. More specifically, you use light filtering glasses or computer software to filter light wavelengths with high specific quantum sensitivities.
  • Additionally, exercising and eating are strong zeitgebers; this means that they are going to affect your body clock a lot.

Further in this course, you will be able to use a calculator to determine the impact your particular lighting situation has on your melatonin. This includes your dark period as well. The most effective range of wavelengths for suppressing melatonin is between around 440 and 530 nm.

The type of light, its intensity and the distance to it also matter. The light wavelength distribution is going to be different. There are also a few other things that you should do during the dark period.

  • First of all, you want to fast at that time. Do not eat anything.
  • You also want to avoid exercising hard during the dark period.

Not doing these will cause your body to believe that it is daytime, which will destabilize your circadian rhythm.

Closing remarks

So, now you know how the general idea of the dark period. You also know how long it should be and what you should avoid doing during it.
In the next lesson, we will take a more in-depth look at how to schedule dark periods on polyphasic schedules.

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

  1. Hmm, I wonder why it says ‘Enroll’ for course & a lock symbol even though I clicked on enroll

    1. You would need to create an account on the website to view everything. If you don’t want to do so, you can see the abbreviated version in the Overview tab.

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