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How does light affect sleep?

Light is one of the biggest environmental factors affecting how we sleep. Yet, the relationship between light and sleep is deeper and more complex than simply turning the lights off at bedtime. There’s a lot we can learn about light, and by adjusting how much and when we’re exposed to it, we can make our sleep environment and bedtime routines better, and get better quality sleep.

Exposure to light stimulates the mind and body, promoting alertness and energy. The light shining through your window early in the morning is particularly helpful, while exposure to light in the evening can pose a problem, making it much harder to fall asleep. Let’s take a look at how light affects sleep.

What type of light affects sleep?

Any kind of light can influence how you sleep, but the impact can vary between different types of light. Natural daylight, generated by the sun, has the biggest influence on sleep and is far more powerful and bright than artificial indoor lighting. While indoor lighting is usually lower than around 500 lux, natural daylight can have up to 10,000 lux.

Artificial lighting has a range of various effects, with different amounts of warmth, illuminance, brightness, and even wavelength having an influence on how our brain perceives the light.

The light we see on most of our electronic devices such as smartphones, tablets, and computer screens is referred to as blue light, although it doesn’t look blue to us. Blue light has a short wavelength and is made up of many LED lights. Studies have shown that blue light has a much more significant effect on melatonin and the circadian rhythm than light with a longer wavelength does. This is why you’ll always hear that if you want better sleep, you should stop using your smartphone, tablet, or computer before bedtime! 

Is it best to sleep in total darkness?

Short answer: Yes!

Unless you’re just trying to take a quick nap during the day and don’t want to fall into a deep sleep, it’s best to create as much darkness as possible to reduce any potential disruptions to your sleep. 

Glowing night lights or lamps can be helpful and reassuring for young children who are afraid of the dark, but as they get older it’s best to try to wean them off so that they too can get their best sleep.

How light affects sleep

Light is arguably the most important factor in our external world that affects sleep, significantly influencing three of the key processes the body and brain goes through when it comes to getting to sleep and staying asleep: circadian rhythm, melatonin production, and sleep cycles.

Light and the circadian rhythm

You may know it as your internal clock, the circadian rhythm regulates and controls the 24 hour sleep-wake cycle. This process is controlled by a small part of the brain called the circadian pacemaker, and is heavily influenced by light and melatonin. When your eyes sense light, this part of your brain sends a signal throughout your body to let all your organs and other systems know that it’s daytime.

In our world of electric lights, screens, and technology, we’re constantly surrounded by artificial light, sending the circadian pacemaker false messages about daylight. The later you’re exposed to light, the more your circadian rhythm will be pushed and altered, so that you sleep later and wake later. It only takes a small amount of light to have an impact on your circadian rhythm. Consider if you were only exposed to natural light: your circadian rhythm would synchronise with the sun as it rises and sets, keeping you awake during daylight hours and signaling your body to wind down at night. 

Light and melatonin

Often referred to as the sleep hormone, melatonin is naturally released by the body when our eyes detect darkness. As the sun goes down and the lights go off, the darkness signals to your brain that daytime is over and it’s time to sleep. Your brain then releases melatonin via the pineal gland, increasing drowsiness and promoting sleep.

Daily cycles of melatonin production help to regulate the circadian rhythm, reinforcing a regular and healthy cycle of sleep and wake times. Exposure to light slows or even stops the production of melatonin, keeping you alert and awake. This is great when you need to be energised during the day, but it makes you vulnerable to the effects of artificial light from lights or screens in the evening.

Light and sleep cycles

Not to be confused with the sleep-wake cycle, of being awake and asleep over 24 hours, sleep cycles refer to the stages of sleep that we go through during a normal period of sleep. You may have heard of rapid eye movement (REM), which is one of these stages. Others include non-REM sleep, slow-wave sleep (SWS), and deep sleep.

Each stage or cycle of sleep usually lasts 70-120 minutes, and each has different characteristics, functions, and benefits. Even if you do manage to fall asleep, exposure to light at night or sleeping with the lights on, can hinder the transitions between the various cycles of sleep, cause you to wake up and interrupt a sleep cycle, and reduce the time spent in deeper, more restorative stages of sleep.

Light and sleep disorders

Circadian rhythm disorders, such as jet lag, occur when someone’s internal clock is thrown off or pushed so far back or forward that they don’t align with their environment or schedule.  

Jet lag

Jet lag occurs after long distance plane travel, when you’ve crossed time zones and arrived in a location several hours behind or ahead of the time zone you started in. The change disrupts the natural circadian rhythm and it takes some time for your body and your internal clock to adjust to the new day and night cycle. People suffering from jet lag struggle to get to sleep, wake up in the middle of the night, or crash during the day, feeling excessively sleepy during daylight hours.

Light is an important aspect to help acclimatise to the new time zone. Exposure to natural daylight and avoidance of light in the evenings helps the process along, eventually realigning the circadian rhythm.

Shift work

Shift work is common in a number professions, requiring people to start and end their work day according to a rotating roster that involves night shift. When working night shift, people must start their work day late in the evening and work through until the early morning. When working night shift, people must get their sleep during the day time. This throws the circadian rhythm off.

Add to this a constantly rotating schedule of both night and day shift, and it becomes impossible to regulate the sleep-wake cycle. Shift workers are at high risk of developing shift work disorder, which causes insufficient sleep, drowsiness during awake times, mood issues, and even increased risk of workplace accidents. Managing exposure to light can aid the recovery from shift work disorder.

How you can use light to get the best possible sleep

Make your bedroom as dark as possible

Thick, blockout curtains will help prevent any street lamps or other outside lights coming in, allowing you to eliminate unwanted light and create an environment that’s as dark as possible.

It’s best to switch off any electronic devices that emit light through the night. Those small lights that go entirely unnoticed during the day, such as the little red lights that indicate “power on” or the blinking light on a router, can produce a persistent glow during the night. Whether or not it bothers you, it could still be disrupting your sleep. If you can’t eliminate those light sources, a sleep mask is a great way to keep the light from affecting your sleep. Simply closing your eyes isn’t always enough.

Minimise light exposure in the evening

While getting ready for bed, dim the lights or reduce lighting to a warm, low-illuminance lamp or two. This can help with relaxation and getting into the right headspace for sleep. 

Some people even like to light candles in the evening, to eliminate artificial light altogether. This can be a very relaxing ritual when accompanied with an evening meditation to wind down. Just be very careful with the open flame.

Introduce a curfew on screen time

Screens that emit that short wavelength blue light keep your brain stimulated and alert. The later you use them, the more likely you are to experience disruptions to sleep and circadian rhythm. Ideally, you would keep your tablet, computer, and smartphone out of the bedroom entirely to eliminate the temptation to reach for your phone to check messages before bed. Yet, even a small reduction in use of these devices can improve your sleep.

You can also turn down the brightness, switch off notifications, and even use tools such as glasses or contact lenses with blue light blocking filters to reduce the impact this artificial light source has on your sleep.

What else you can do to improve sleep

In addition to controlling your light exposure and understanding how it affects your circadian rhythm, melatonin production, and sleep cycles, there are other steps you can take to improve your sleep, such as getting regular daily exercise, avoiding caffeine, and sticking to regular wake-up and bedtimes.

If you have ongoing problems with sleep that affect your energy, mood, or day-to-day life, or a circadian rhythm disorder such as jet lag or shift work disorder, you should seek professional help from a doctor.

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