man sitting in bed with lights on
Sleep Health

Light And Sleep: How Light Affects Sleep Quality

  •  Purple Author Icon
    Last Updated
    July 31, 2022
    min read

    It’s common knowledge that dim light during bedtime helps you fall asleep easier, but diving deeper into this simple truth reveals the relationship between levels of light and sleep disturbance. The science behind the light conditions of your surroundings now shows it's absolutely impactful on your quality of sleep.

    Our guide will take you behind the body’s internal body clock and the outside forces that affect the overall quality and duration of your sleep. We’ll teach you how to limit your exposure to blue light, the concept of adenosine levels, and how to keep your sleeping space in relatively comfortable darkness to help you achieve a natural transition to REM sleep.

    How Does Light Affect Your Sleep

    Your sleep quality can be drastically affected by the amount and kind of light you’re exposed to in your sleeping space. Three major elements of sleep are directly affected by the light conditions of your surroundings: your circadian rhythm, melatonin levels, and sleep cycle phases. 

    The Circadian Rhythm

    The circadian rhythm is the internal 24-hour clock that governs your body activities, including sleep. A part of the brain known as the "circadian pacemaker" controls this natural rhythm and is directly influenced by light exposure. From sunrise to sunset, your body follows the Circadian Rhythm to transition between activity and rest.

    Why? Because light is a stimulant for your brain. When light enters the eyes, signals are sent to the brain that trigger alertness and observation. 

    The kind of light you're exposed to also affects your circadian clock. Studies show that exposure to artificial light may be harmful, and not just because it throws your sleep patterns off. In one study conducted over a five-year period, women who slept with a light or TV on were considerably more likely to gain 10 pounds or more, even after controlling for factors related to diet and exercise habits.

    Melatonin Levels

    Melatonin is a hormone produced by the pineal gland in response to dark environments. As the Melatonin builds up in your brain, it triggers sleepiness as part of your natural sleep cycle. This comes together in what we call the circadian melatonin rhythm or your body's natural schedule for producing this hormone. 

    Since melatonin secretion is directly related to light conditions and light intensity, ensuring you have a dimly lit sleep environment keeps your melatonin in check.

    Sleep Cycles

    Though everyone sleeps, not all kinds of sleep are the same. Research shows that a person goes through four to six sleep cycles that last about 70 to 120 minutes each. The most important sleep cycles are the ones that give you truly restorative rest, such as Rapid Eye Movement (REM) sleep.

    However, with higher light levels, your natural sleep cycles could be disrupted, leading to rougher transitions between these stages. Overall, exposure to light may throw off your circadian clock.

    What Causes Light-Induced Sleep Disruption?

    One of the effects of light on humans is that it stimulates brain activity. That can be challenging in this day and age no thanks to artificial light. Since exposure to light delays the secretion of melatonin, scrolling through social media within an hour before bed could keep you awake and active much later into the evening.

    What Types Of Light Affect Sleep

    Most devices today emit what is known as Blue Light. On the spectrum of light, blue wavelength light is emitted from screens and the sun. It can actually be beneficial in the daytime – this kind of light can boost your reaction time, attention span, and mood. However, exposure to late-night screen time hours before bed proves detrimental to your sleep.

    Blue light is also a short-wavelength light, meaning its frequencies hit your eyes at a faster rate at higher energy compared to other colors on the light spectrum. Nighttime light exposure breaks your body's natural transition to a resting state – this might explain the feeling of restlessness after using phones before sleeping. 

    Is It Bad To Sleep With Lights On?

    A recent study has shown that even just a bit of light during sleeping time isn't good for you. But with technology becoming an unavoidable presence, it can be difficult to avoid light at night. In fact, most people sleep in rooms with a fair amount of artificial light, thanks to devices like laptops, televisions, or phones. 

    If you are exposed to bright evening light within two hours before bedtime, you’ll have slightly higher brain activity in the evening. This means you stay up later throughout the night and wake up later in the morning.

    This can prove difficult for those who work the night shift. Working evening hours with bad light conditions could prove detrimental to your overall health. 

    In 2018, the Bureau of Labor and Statistics in the U.S. estimated that around 16% of workers in America work the night shift. That's a considerable number of the workforce who typically sleep during the daytime and are at risk of incurring a sleeping disorder.

    Can Certain Levels Of Light Exposure Improve Sleep?

    Ambient lighting can help you set up in the evening, and there are specific light conditions that can stimulate better sleeping time. Dim red lights make great night lights, as they're less likely to shift your circadian rhythm.

    How Come Certain People Can Sleep With Lights On?

    Light conditions differ from person to person and room to room. A study from Northwestern Medicine shows that a significant proportion of individuals (up to 40%) sleep with a bedside lamp or other light source on in the bedroom, despite the science showing that darkness is beneficial for optimal sleep.

    However, several factors can explain how some people fall asleep, even with the lights on. For example, they may be in the process of correcting their body clock after an all-nighter or have already acclimated to low lighting.

    How Can Darkness Influence Sleep?

    A dark room helps with sleep because light sources stimulate your brain, which in turn encourages your body clock to keep ticking a little longer than scheduled. Melatonin, which encourages sleepiness, is released by your "circadian pacemaker" directly in relation to your exposure to darkness.

    Ways To Create A Darker Room

    One of the best ways to improve light conditions in your resting quarters is to install blackout curtains on the windows. These are specially designed to keep most, if not all, natural light from entering your room. If you absolutely need to have a night light (either for kids or yourself), make sure to get very dim lights on the red spectrum.

    Apart from keeping the lights low at night, there are other things you can do right now to make your sleeping quarters a better space for rest.

    Frequently Asked Questions About Light And Sleep

    Does exposure to light cause insomnia?

    Light by itself won't cause insomnia, but a very specific kind of light can keep you up later into the evening. Exposing yourself to short-wavelength light such as blue light – like those found in devices – will make it harder for your body to transition to sleep. 

    The intensity of light found in your sleeping space will also prove detrimental to your circadian rhythm. Remember, your body must transition neatly through the sleep cycles to provide you with quality sleep. Having a room with lighting similar to the outdoors during the day will make that natural flow much harder to achieve.

    What light helps with sleep?

    Strictly speaking, any kind of lighting can be a stimulus for your brain. But if you need light to sleep, ambient lighting or dim red lights are the safest bet. They have longer wavelengths and are not as disruptive as the harmful blue light found on your screens.

    Will sleeping with the lights on affect your eyes?

    Being a brain stimulant, sleeping with the lights on makes it more challenging for your body and mind to transition towards truly restful sleep. However, some people may feel safer or more comfortable with a bit of light on. At the end of the day, whatever helps you sleep at night will always be the better and healthier option.


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