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How Light Affects Our Sleep: Daylight vs. Artificial Light


Different types of light have different effects on us and our biological clock. It is natural to be exposed to bright daylight when we wake up, and various processes in our body follow the day-night rhythm, where the day is activity time and night is the time for rest.

Artificial lights from lightbulbs and screens have been proven to decrease the levels of hormones which make us sleepy. We stay alert and awake for a longer period of time, with poorer sleep quality compared to when there is no artificial light exposure.

Even though we can’t escape artificial light, it is important we know what it does to us. It is then that we can consider making certain changes to our environment and significantly reduce the negative effects of light exposure.

Light and circadian rhythm

We all have an inner biological clock which regulates our sleep patterns, hormone discharge, peak productivity, and various processes in our body. This is known as our circadian rhythm. When the morning light hits our eyelids, the light receptors in our eyes take that message and send it over to the hypothalamus in the brain, which then prepares our body for waking up. The hypothalamus plays many roles, one of which is circadian rhythm regulation.

As the lights get low in the evening, the hypothalamus orders the production of melatonin, our sleep hormone, whose levels keep increasing as we grow more tired and finally fall asleep. As the sun always rises and sets at about the same time (seasonal changes are occurring very slowly), we are naturally given a steady sleep-wake rhythm. Such a rhythm lessens the chances of having and developing sleep problems, hormone imbalances, weight gain, and other health and mood disorders.

Our illuminated, active part of the day had prolonged quite a lot compared to about a hundred years ago. Now, as the sun is setting, we turn on the lights and have them on until late at night. Even after turning them off at bedtime, many people continue using their smartphones.

This huge change to our natural rhythm couldn’t go without consequences. Lights, especially LED and screen lights, tend to confuse our circadian rhythm so our body can’t get sleep at the proper time. It can’t ‘catch up’ with this rhythm over the night, and many of us wake up tired and remain excessively sleepy throughout the day.

Natural light leads to better sleep and more happiness

When we are exposed to sunlight sufficiently, our serotonin levels rise. Serotonin works as a neurotransmitter, making us happy, and as a hormone, helping with melatonin production. As daily light dictates our circadian rhythm, we are more likely to have a good night’s sleep.

In some countries, light exposure during winter decreases significantly due to shortened days and overcast sky. Many suffer from winter depression or seasonal affective disorder (SAD) at that time. Recently, light therapy has been used to improve mood, sleep, and cognitive functions.

In light therapy, special light therapy boxes are used. They are kept inside the room, next to the person who is undergoing the therapy, and are designed to mimic natural light in order to boost mood and improve sleep.

Although a useful choice when daylight is scarce, light therapy cannot replace the benefits of bright light in the morning and afternoon. Daylight helps with vitamin D production, which makes our bones and immune system stronger.

Artificial lights at night and the risk of sleep disturbances

As much as it is important to be exposed to bright light during daytime, it is also important to limit artificial nighttime lighting. Bright light ‘tricks’ our hypothalamus, so it reacts to it as if it were daylight. Therefore, instead of producing melatonin and making us sleepy, our bodies stay alert even late at night.

And while we will eventually start feeling tired and worn out (due to adenosine buildup in the brain), you may still have trouble falling asleep. A common mistake people do is taking a phone into their hands hoping it will help them fall asleep – but it won’t, the problem will only be worse.

Being surrounded by bright lights leads to circadian rhythm disturbances, like insomnia (defined as an inability to begin and/or maintain sleep), excessive daytime sleepiness, sleep-wake patterns that are too different from those of society, and social jet lag.

How do lights at work affect our sleep and health?

Numerous studies were dedicated to how working in shifts affects the lives and health of workers. For example, office workers who have no access to daylight during their working hours have poorer quality and shorter duration of sleep compared to those who work in well-lit offices with windows.

Not only is their sleep affected, but those who are exposed to daylight also tend to be more physically active and happy/satisfied with their life. They make fewer errors at work and are more productive. Lack of natural light increases health issues and depressive behaviors.

Another study that aimed at understanding the impact of lights at work observed nurses. They switched work shifts between night and day – in the first nights after the switch, they would report increased sleepiness, followed by impaired thinking. Upon filtering short wavelengths from their work light, a noticeable improvement was found – they reported fewer sleep problems and faster transition ability from one shift to another. The researchers concluded that their circadian rhythms were not being shifted as when long-wavelength lights were used.

Sleeping with a light on

The negative effects of lights on our body are not only present when we are awake, but also when we sleep. A 2018 study published in the journal Sleep has compared insulin levels of two groups of people – one that slept in dark for two nights, and one that slept in dark on the first night and with a 100 lux light on the second night.

In the morning, upon testing, the group which slept with the light on has had abnormally high insulin levels. Their insulin resistance was similar to those in the prediabetic state, and based on this, the study researchers have concluded there is a possibility that long-term night light exposure affects metabolic function.

Insulin is also known to be high in those who cut back on sleep – perhaps we could draw a parallel between sleep deprivation and sleeping with a light on.

Health problems linked with lights

Artificial light also impacts thermoregulation, blood glucose levels (creating insulin resistance), and blood pressure. A study has linked artificial light exposure and low melatonin to cardiovascular diseases, and there is an indication that low melatonin somehow may be connected to cancer.

Artificial lights are proven to impact sleep onset and quality, which are linked to hormone imbalances. As a consequence of chronic hormonal changes, we are likely to suffer from mood disorders, weight gain, cardiovascular problems, and infertility. Reproductive hormones are very susceptible to sleep and can easily get disturbed.  

As the brain doesn’t get the chance to have a night of restorative, restful sleep, it also doesn’t clean from the plaque whose buildup is associated with Alzheimer’s disease.

How to get away from artificial light

Therefore, in order to get away from too much light, we first have to learn what things to avoid. White and blue light is found in:

  • TV’s, light bulbs, and digital clocks with LED
  • Computer screens
  • Smartphone, e-reader, and tablet screens
  • Other gadgets

About two hours prior to sleep, you should dim the lights and spend some time in the quiet, calming atmosphere. Reading a book instead of using a phone is a lot better solution. The National Sleep Foundation recommends low-wattage, incandescent light bulbs near the bed.

Stop using technology before bed. This means no TV, computers, or phones. If you have to work on a computer until late at night, there is a way to protect your eyes from the blue light.

  • Install f.lux. It is a free computer program designed to alter the colors of your computer and match the daylight, easing eye strain while working. It adds orange hue to cancel out the blue light.
  • Use blue-light blocking eyeglasses. They are proven to help guard the eyes and allow melatonin production.

Make sure that your room is completely dark when you go to sleep. If there are light buttons or small lights coming from your computer, digital clock, or TV, turn them away or block them with thick, black tape or an object. Also get good, thick curtains. You can invest in a sleep mask in case you cannot make your room dark enough.

Additional Resources

  1. Blue light has a dark side. Harvard Health Publishing. May 2012. https://www.health.harvard.edu/staying-healthy/blue-light-has-a-dark-side Accessed January 13, 2019.
  2. Gooley J.J, Chamberlain K, et al. Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans. The Journal of Clinical Endocrinology & Metabolism. March 1, 2011. https://academic.oup.com/jcem/article/96/3/E463/2597236 Accessed January 13, 2019.
  3. Pilorz V, Tam S. K, et al. Melanopsin Regulates Both Sleep-Promoting and Arousal-Promoting Responses to Light. PLOS Biology. June 8, 2016. https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002482 Accessed January 13, 2019.
  4. Duffy J.E, Czeisler C.A. Effect of Light on Human Circadian Physiology.
    Sleep medicine clinics. June 2009. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2717723/ Accessed January 13, 2019.
  5. Mason I, Grimaldi D, et al. Impact of Light Exposure during Sleep on Cardiometabolic Function. Sleep. April 27, 2018. https://academic.oup.com/sleep/article-abstract/41/suppl_1/A46/4988151?redirectedFrom=fulltext Accessed January 13, 2019.
  6. Boubekri M, Cheung I.N, et al. Impact of Windows and Daylight Exposure on Overall Health and Sleep Quality of Office Workers: A Case-Control Pilot Study.
    Journal of clinical sleep medicine : JCSM : official publication of the American Academy of Sleep Medicine. June 15, 2014. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4031400/ Accessed January 13, 2019.
  7. Rahman S. A, Shapiro C. M. Effects of Filtering Visual Short Wavelengths During Nocturnal Shiftwork on Sleep and Performance. Chronobiology international. July 8, 2013. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3786545/ Accessed January 13, 2019.

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