Understanding the Light-Dark-Cycle — 4 Tricks to Hack Your Sleep

Science-based content to increase your performance

Feb 18, 2019 · 11 min read

Light and Darkness

After reading this article, you’ll have understood how light and darkness influences your sleep and how to leverage that knowledge to fall asleep faster and sleep healthier. You’ll also have learned what the difference between artificial and natural light settings is — and why this difference is relevant for you.We’ll explain how you can improve sleep quality and daily productivity significantly by:

  1. Applying blue light in the morning to regulate your hormone cycle
  2. Applying blue light to boost concentration for specific activities
  3. Dimming lights one hour before you go to bed
  4. Leveraging vitamin D3 to sleep better and feel more alert

This article explored how hormones influence our sleep to a great extent. Yet, which factors do influence our hormones? While external events and substances, such as workouts or coffee play a major role, the two most important factors are light and darkness [1].

While many know that there are certain hormonal rhythms that lead to us getting hungry, feeling alert and feeling tired, rarely are people aware of how heavily these rhythms are influenced by light and darkness. To demonstrate this, let us highlight a famous experiment that was conducted to proof the influence of those two factors by investigating two groups: One group that was completely isolated from variation in light and darkness; and another group that was exposed to a similar environment with natural variations in light and darkness. That is, the sun was setting in the evening and rising in the morning.

The light-dark-cycle

Figure 1: Sleep cycles for different probands; Source: https://www.trilux.com/de/beleuchtungspraxis/innenraumbeleuchtung/allgemeine-anforderungen/licht-und-nicht-visuelle-wirkungen/der-circadiane-rhythmus-und-die-innere-uhr/

Unfortunately, this diagram exists only in German, yet it is significant enough to be highlighted by means of our article anyway. It indicates in blue when people are asleep. The left (control) group was exposed to normal lighting and hence stuck to a regular bedtime and wakeup period with slight exceptions during the weekend. The other group, yet, which was isolated from variations in light and darkness, was able to stick with their rhythm for only three days. Afterwards, their rhythm started to shift consistently until it was turned completely upside down. This seems just as if our natural wake-cycle is longer than 24 hours. It actually is:

“The spontaneous circadian awake/sleep cycle is 25 hours, slightly longer than the body temperature cycle, but when subjects are exposed to environmental synchronization, the two cycles coincide. In individuals undergoing temporal isolation, the two rhythms become independent often leading to subjective discomfort and fatigue.” [2]

Disturbing Your Light-Dark-Cycle Has Severe Consequences

Hence, yes, rhythm is important. Effects reach much farer than mere discomfort and fatigue. Especially shift workers, those suffering most from disturbances in light-dark-cycles, report higher risk of heart attacks and higher risk of cancer of about 15%. [3] Sustained night work was furthermore linked to 50–100% higher risks of breast cancer for nurses and many other diseases such as diabetes, cardiovascular risks, obesity, mood disorders and age-related macular degeneration. [4][5]

Our world is incredibly ‘light-polluted’. The natural light-dark-cycle, which was earlier imposed by the sun, does not longer exist in our lives. Yet, as a product of evolution, it has been programmed over tens of thousands of years into our intricate biological workings. As the experiment above demonstrated, it takes only three days of disturbance for our body to experience serious consequences. Yet, just regulating our exposure to light won’t be enough. There are great differences between artificial and natural light.

Natural vs Artificial Light

To name just some benefits of sunlight, it helps us to maintain more energy during the day, regulate blood pressure, be in a better mood, foster anti-ageing and prevents diabetes, cancer and heart diseases. [6] This sounds a little bit too sophisticated. At the end of the day, are we not just speaking about ‘light’? Frankly, all of these benefits are because of a little hormone-like vitamin: Vitamin D3 — secreted by our skin when exposed to sunlight. There are even indications that vitamin D3 helps boost our memory and strengthens our ability to solve puzzles. [7] Hence, let’s dig a little deeper into how vitamin D3 works and how we can naturally get more of it.

Vitamin D3 and Food

First of all, while many believe that we could eat food containing enough vitamin D3, the truth is a little bit more complicated. To reach a minimum level, we would have to drink about 22 liters of milk and eat about 5 kilograms of fish — every day. Considering the fact that our stomach would simply explode from trying this, let us have a look at a valid alternative: naturally secreting vitamin D3 by exposure to sun light.

Facts About Vitamin D3 Secretion

How much sunlight a day do we need? What happens if we spent some days completely deprived from sun? How do we secrete vitamin D3? Let us list the most important facts about vitamin D3 below:

  • Vitamin D3 is secreted by our skin if it is exposed to enough sunlight. We should hence expose as much of our skin to sunlight as possible if we want to maximize vitamin D3 secretion. We want to be aware, though, that too much exposure to sun can have negative effects on your health. [6]
  • Vitamin D3 can only be secreted if sunlight is strong enough. North of the latitude of Barcelona (approximately 42nd), vitamin D3 can only be secreted during summer. We can use our shadow to test whether vitamin D3 secretion is possible: If our shadow is as long as us or even longer, vitamin D3 secretion is not possible. [8]
  • Vitamin D3 is stored in our body up to 6 months. We can thus ‘charge’ up in the summer to ‘save’ for the winter. [8]
  • Vitamin D3 has significant influence on our inner clock and can be a fantastic means of inhibiting jet-lag. [9]
  • Vitamin D3 inhibits melatonin secretion. [10]

How much vitamin D3 is secreted in our skin if we expose our skin to sunlight? Below is a table that adds clarity.

Vitamin D-Synthesis During a Sunny Summer Day*

*All of those numbers are merely benchmarks and vary based on age, skin type and time of the day.

Leading scientists confirm that we need up to 100 micrograms a day [11], which means that a sunny holiday of spending 14 days at the beach might be enough for the entire year. Yet, especially if you do not spend your holidays being exposed to a lot of sun, you should consider getting enough time a day in the sun or even supplement vitamin D3. We want to emphasizehere, though, that this figure is highly debated among researchers. Given our thorough research, 100 micrograms a day is the number we can comfortably recommend.

When supplementing vitamin D3, make sure to do so in the morning, as it inhibits your melatonin production and thus might have detrimental effects on your sleep. Furthermore, being exposed to sun in the morning helps regulating your hormones greatly; firstly, because of vitamin D3, which clears melatonin and makes you feel alert and secondly because of the exposure to natural sun light. Try to eliminate inhibitors, such as sunscreen and soap, both of which mitigate vitamin D3 absorption. [12]

Sunlight and ‘white’ office light has a higher proportion of ‘bluelight’, which is a natural inhibitor of melatonin. Its function is of course to make us awake and feel alert, an effect that worked perfectly in the past as there was no strong light once the sun had set. However, since the invention of electricity, we built strong artificial sources of light that inhibit our melatonin production quite significantly. Especially the screens of our phones, TVs and PCs emit a light with a high proportion of bluelight, which inhibits melatonin production to a great extent. A good benchmark is to reduce exposure to bluelight and dim lights at least two hours before going to bed. In the best case, sources of bluelight should be eradicated completely one hour before falling asleep.

There are great tools that help you along the way. F.lux can filter bluelight entirely and simulate sunset on your PC. Moreover, apple and Android phones usually have built-in apps that filter bluelight in the evening.

After having worked through a vast theoretical background, let us quickly state what this means practically for you.

1. Expose Yourself to Blue Light in the Morning to Regulate Your Hormone Cycle

Make sure you do not spend too much of your morning in darkness. This does not only make you feel more tired, it also interferes with your natural light-dark-cycle. That can have consequences that reach far beyond mere tiredness. You might have trouble falling asleep in the evening or even feel less hungry and energetic during the day.

2. Apply Blue Light to Boost Your Concentration for Specific Activities

Blue light stimulates you. While that is bad when winding down in the evening, those stimulating effects can be just as useful as a coffee to boost your performance when needed. It can also be combined with coffee as bluelight triggers different physiological effects. Our recommendation is: Get a daylight lamp (1 and 2). And go out during lunch time. Sun is strongest at noon and so is vitamin D3 absorption as a corollary.

3. Dim Lights One Hour Before You Go to Bed

During this article, we explored how important it is to de-stress in the evening, especially right before going to bed. Dimming lights strongly contributes to that. Our pro-tip is to use candles: not only does that lead to better sleep, it is also quite romantic. As we learned, bluelight (over)stimulates your body and decreases melatonin secretion. Again, those effects can reach far beyond just diminishing your sleep quality. When your hormone cycles are disrupted and your sleep quality is low, it is much more likely for you to get ill and develop diseases such as dementia and cancer. A last tip from us is to reduce exposure during the day gradually if possible. A study showed that sudden changes of light, both when going to bed and waking up, led to worse results than gradual changes. [13]

Even though we dim lights in the evening and want to reduce exposure to sources of bluelight, it is very unrealistic to not use our laptops and phones when going to bed. Thankfully, apps such as f.lux are free and simulate sunrise and sunset on our phones by filtering bluelight off our screen. We recommend setting the reduction of bluelight in your preferences to a maximum level when using f.lux.

4. Leverage Vitamin D3 to Sleep Better and Feel More Alert

Vitamin D3 does not only lead to better sleep. It makes you feel more alert, reduces your risk of getting sick and greatly improves your mood. Therefore, it is sometimes also known as the happiness vitamin. We can only recommend to go out at lunch and pay attention to your exposure to natural sunlight. One hour a day during Summer is a good rule of thumb. As stated above, the benefits of doing so are enormous. If you do want to supplement vitamin D3, we recommend you do so in the morning and take up to 4000 IU / 100 mg for at least one week.

Our bodies are programmed to respond to signals of light and darkness since tens of thousands of years. Only recently do we understand the issues adjacent to chaotically manipulating these signals as we please. Giving our body what it naturally needs and requires is easily achieved by integrating those 5 steps into our set of routines. For this week, we encourage you to try all of them and be fascinated by how easy sleep can be.

Note that this is article one in a whole series of articles. You can find the subsequent articles on our website. After you have read our articles, not only will you have a thorough understanding of your body and your inner workings, but also will you be able to put that knowledge into use and apply it flexibly throughout your live to design your individual desired plan of winning life.


[1] Zawilska, J.B. (1996). Melatonin as a chemical indicator of environmental light-dark cycle. Acta Neurobiologiae Esperimentalis, 56, 757–767. Retrieved from https://pdfs.semanticscholar.org/7950/a37963605cdd7c3c8c97dc0dc6c201bffe8b.pdf

[2] Onen, S.H., Onen F., Bailly, D., & Parquet, P. (1994). Prevention and treatment of sleep disorders through regulation of sleeping habits. Presse Medicale, 23(10), 485–489. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/8022726?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum

[3] Parkes, K. (2017). Shiftwork and Health. In S., Ayers, C., McManus, & J., Newman (Eds.). Cambridge Handbook of Psychology, Health and Medicine(3rd ed., pp. 1–16). Cambridge, UK: Cambridge University Press.

[4] Touitou, Y., Reinberg A., & Touitou, D. (2017). Association between light at night, melatonin secretion, sleep deprivation, and the internal clock: Health impacts and mechanisms of circadian disruption. Life sciences, 173,94–206. doi: 10.1016/j.lfs.2017.02.008.

[5] Hintzpeter, B., Mensink, G. B. M., Thierfelder, W., Müller, M. J., & Scheidt-Nave, C. (2007).Vitamin D status and health correlates among German adults. European Journal Of Clinical Nutrition, 62(9), 1079–1089. doi: 10.1038/sj.ejcn.1602825

[6] Rhee, H., Vries, E., Coomans, C., Velde, P. & Coebergh, J. (2016). Sunlight: For Better or For Worse? A Review of Positive and Negative Effects of Sun Exposure. Cancer Research Frontiers, 2(2). 156–183. doi: 10.17980/2016.156.

[7] Soni, Maya & Kos, Katarina & A Lang, Iain & Jones, Kerry & Melzer, David & Llewellyn, David. (2012). Vitamin D and cognitive function. Scandinavian journal of clinical and laboratory investigation. Supplementum. 243. 79–82. 10.3109/00365513.2012.681969.

[8] Wacker, M., & Holick, M. F. (2013). Sunlight and Vitamin D: A global perspective for health. Dermato-endocrinology, 5(1), 51–108.

[9] Mccarty, David & L Chesson, Andrew & K Jain, Sushil & Marino, Andrew. (2013). The link between vitamin D metabolism and sleep medicine. Sleep medicine reviews. 18. doi:10.1016/j.smrv.2013.07.001.

[10] Golan, D., Staun-Ram, E., Glass-Marmor, L., Lavi, I., Rozenberg, O., Dishon, S., Miller, A. (2013). The influence of vitamin D supplementation on melatonin status in patients with multiple sclerosis. Brain, Behavior, and Immunity, 32, 180–185. https://doi.org/10.1016/j.bbi.2013.04.010

[11] Heaney, R. P. (2005). The Vitamin D requirement in health and disease. The Journal of Steroid Biochemistry and Molecular Biology, 97(1–2), 13–19. https://doi.org/10.1016/j.jsbmb.2005.06.020

[12] Binkley, N., et al. (2007). Low vitamin D status despite abundant sun exposure. Journal of Clinical Endocrinology And Metabolism, 92(6), 2130–2135. doi: 10.1210/jc.2006–2250

[13] Kondo, M., et al. (2007). Combined influences of gradual changes in room temperature and light around dusk and dawn on circadian rhythms of core temperature, urinary 6-hydroxymelatonin sulfate and waking sensation just after rising. Collegium antropologicum, 31(2), 587–593. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/17847944

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