To eliminate any trouble sleeping and get a handle on your sleep hygiene, you need to understand the importance of light and its effects on your sleep. Light influences our circadian rhythm, melatonin production, and sleep cycle.

How does light affect our circadian rhythm?

The circadian rhythm is a 24-hour internal clock that coordinates a number of processes in our bodies, including sleep. The circadian pacemaker controls this rhythm. This circadian pacemaker is a small area of the brain, influenced by exposure to light.

When light enters the eye, it is picked up by the retina. It travels to the brain and signals to the brain about the time of day. The brain then sends signals throughout the body to control organs and other systems in accordance with that time of day.

When exposed to only natural light, a person’s circadian rhythm aligns with the sunrise and sunset, staying awake during the day and sleeping when it’s dark outside. We are exposed to multiple light sources due to the tech-fuelled world we live in today. These affect our brain’s circadian pacemaker.

The way light alters circadian rhythm depends on the timing of light exposure. Exposure to light early in the morning brings our sleep schedule forward. Light exposure in the evening pushes our sleep cycle out to later.

Circadian effects vary based on the type of light and the duration of exposure. Even short periods of artificial light can affect circadian rhythm.

Circadian rhythms are also related to our mood and mental health. For example, seasonal affective disorder is a type of depression that most commonly affects people who live in areas where winter months have very short days. Reduced daylight can interfere with circadian rhythm, contributing to mood changes during the winter.

How does light affect melatonin production?

Melatonin is a naturally occurring hormone in our bodies. The pineal gland in the brain initiates the production of melatonin in response to darkness, and slows down the production of melatonin in response to light. Consistent daily production of melatonin regulates the circadian rhythm, supporting a stable sleep cycle.

How does light affect sleep cycles?

In a healthy night’s sleep we experience four to six sleep cycles, of multiple sleep stages. These include rapid eye movement (REM) and non-REM sleep. If we are exposed to light at night our sleep cycles become disrupted. This then reduces the quality of our sleep. Too much light can can cause us to wake up regularly, interrupting our sleep cycle and reducing the time we need in deeper, restorative sleep stages.

What types of light affect sleep?

Daylight is far more intense than indoor lighting and therefore has a major impact on sleep. To reach a healthy sleep cycle that kicks in with the night sky, you need to ensure you are exposed to daylight each day. Blue light, which comes from mobile phones and computer screens, has a significantly larger effect on melatonin and circadian rhythm than any other indoor light. Therefore blue light can contribute to sleep disorders if we are on our screens too close to bedtime.

How can you adjust your environment & routine to get the best sleep?

In this modern world, a good night’s sleep is a luxury for some. Sleep is one of the most important drivers of our physical and mental health. It affects every aspect of our lives and should be a key wellbeing priority for us all. But many of us have trouble sleeping.

At nighttime, when we finally stop and become still, this is when our minds tend to race. Our Sleep Ritual Guide that we created with lifestyle coach Pat Divilly is filled with practical tips and tools to help calm the mind and relax the body.

 

References:

1. Dodson, E. R., & Zee, P. C. (2010). Therapeutics for Circadian Rhythm Sleep Disorders. Sleep medicine clinics, 5(4), 701–715.https://doi.org/10.1016/j.jsmc.2010.08.001

2. Fonken, L. K., Workman, J. L., Walton, J. C., Weil, Z. M., Morris, J. S., Haim, A., & Nelson, R. J. (2010). Light at night increases body mass by shifting the time of food intake. Proceedings of the National Academy of Sciences of the United States of America, 107(43), 18664–18669.https://doi.org/10.1073/pnas.1008734107

3. Wright, K. P., Jr, McHill, A. W., Birks, B. R., Griffin, B. R., Rusterholz, T., & Chinoy, E. D. (2013). Entrainment of the human circadian clock to the natural light-dark cycle. Current biology : CB, 23(16), 1554–1558.https://doi.org/10.1016/j.cub.2013.06.039

4. Chang, A. M., Santhi, N., St Hilaire, M., Gronfier, C., Bradstreet, D. S., Duffy, J. F., Lockley, S. W., Kronauer, R. E., & Czeisler, C. A. (2012). Human responses to bright light of different durations. The Journal of physiology, 590(13), 3103–3112. https://doi.org/10.1113/jphysiol.2011.226555

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