4 Oct 2016

Difficulty sleeping: Why darkness matters

When it’s been a long day of work, the last thing you want when you go to bed is to find a strip of light sneaking through the curtains, falling on your face. You’re debating with yourself about whether you should get up and pull the curtain or leave it and roll over…
The reason this situation is so frustrating to many people is because light has a profound effect on sleep - it can cause difficulty sleeping and leak into daytime sleepiness. Light stimulates the body and mind, encouraging wakefulness, alertness and energy, which is why it’s no good to you at night.

Being exposed to light in the hours leading up to and during sleep can pose a serious problem for healthy, abundant, refreshing sleep. Insufficient darkness throughout the night can also lead to frequent and prolonged awakenings and daytime tiredness.

Darkness and melatonin

Darkness is essential to quality sleep. The absence of light sends a critical signal to the body that it is time to rest. So when it’s time to go to bed and you have a strip of light falling across your face, it alters the body’s internal “sleep clock”—the biological mechanism that regulates sleep-wake cycles—in ways that interfere with both the quantity and quality of sleep.

Melatonin, a hormone produced in the brain’s pineal gland, is often known as the “sleep hormone” or the “darkness hormone2.” Melatonin influences sleep by sending a signal to the brain that it is time for rest. This signal helps initiate the body’s physiological preparations for sleep—muscles begin to relax, feelings of drowsiness increase, body temperature drops.

During the evening, melatonin levels naturally rise during as darkness falls and continue to climb throughout most of the night, before peaking at approximately 3 a.m. Levels of melatonin then fall during the early morning and remain low during much of the day. Evening light exposure inhibits the naturally timed rise of melatonin, which delays the onset of the body’s transition to sleep and sleep itself.

The presence of light during the evening increases the chances of you having difficulty sleeping as it directly affects your melatonin production.

Light causing difficulty sleeping

The invention of electricity in the 20th century fundamentally changed our relationship to light and dark, and created in us difficulty sleeping. Artificial light wreaks havoc on sleep without many people even being aware of its negative effects. The widespread use of digital technology—and the blue light emitted from all those screens—has introduced another highly disruptive challenge to sleep.

Measuring light: lux and lumen

Understanding how light is measured can help you manage your exposure to light more thoughtfully, in order to reduce the level of difficulty you have sleeping. There are a couple of measurements that are important in the world of light and dark: lumen and lux.

Lumen: The measurement of light intensity or brightness at the source of the light itself. As light moves from its source, it disperses and its intensity changes. So when you’re thinking about your exposure to light, it’s not just the intensity of light itself that matters, it’s also your distance from the light. That’s where lux comes in.

Lux: Lux takes lumen values and factors in the surface area over which light spreads. Lumen values can tell you how bright a light bulb is, while lux values can give an indication of how bright that light is in the space in which it resides.

Indoor and outdoor lux

Lux can be used to measure all types of light, both natural light and artificial light, and these values can vary tremendously depending on both the source of light, its power, and its proximity.

A sunny summer’s day would have a range of 150,000 lux, while an overcast winter’s day might as low as 1,000 lux.

A typically-lit home, with lamplight and overhead light, as well as light from outside, may have lux readings in the range of 300-500.

Appropriate lux for pre-bedtime activities in the evening, like reading, should be less than 180 lux. This level of brightness will allow you to be quietly active but won’t impede your body’s progress toward sleep. After light’s out, your bedroom should be dark, with lux no higher than 5.

Right light for sleep

Managing your exposure to light in your home and in your bedroom is fundamental to creating a healthy sleep environment. The best thing you can do for your sleep is to look at your bedroom environment and make simple changes there. Make sure window coverings are heavy enough to fully block light, and are well fitted to avoid slivers of streetlight or early morning sunlight from filtering in. Even brief exposure to light can interfere with sleep.

Nightlights can help

If you need a source of light during the night—to make your way comfortably to the bathroom or to a child’s bedroom—use a nightlight with a red bulb.

Red is a long wavelength light that has been shown less disruptive to sleep than other light wavelengths. Put the nightlight in a hallway or another room, if possible. Having a small light in place will help you avoid having to flood your middle-of-night environment with unwanted, sleep-disrupting brightness.

Ways to create darkness

Your body needs time to prepare for sleep, so a sleep routine that includes a gradually darkening environment can help. Dim the lights a full hour before bedtime to encourage your body to begin its physiological progression toward sleep. Here are tips to create darkness in the hours leading up to bed:

  • Use a dimmer switch on overhead lights to control their brightness, or install low-watt, dimmable bulbs in lamps.
  • Avoid screen time the hour before bed: turn off the television, power down computers and tablets, and put your phone away for the night. The light from digital devices contains high concentrations of blue light, a wavelength of light that research has shown is especially detrimental to sleep.
  • Wearing an eye mask worn at night can help deepen darkness and protect against intrusive light. Choose a mask that is soft, comfortable, and flexible. Wearing an eye mask can take a little getting used to, but it is a highly effective tool for limiting your light exposure at night.

Being aware of light’s effects on the body will lead you to pay more attention to the light that surrounds you, both day and night. For a comprehensive guide to improving your sleep, download “Unlocking the Pillars of Health” eBook. By taking time to ensure that your sleeping environment is optimised for sleep, you’re already on your way to protecting and improving your nightly rest.

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  1. Sleep Health Foundation. http://sleephealthfoundation.org.au/pdfs/melatonin.pdf