Light & Darkness: How Do They Affect Sleep?

By Mario Esposito
Last Updated: July 26, 2018

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Light and the absence of it affect the way you sleep more than you know. Human bodies have a built-in physiological response to light and darkness, which aids in the regulation of the sleep-wake cycle.

How Does the Body Respond to Light?

Exposure to light stimulates the body and encourages the need to be alert and awake—whether we like it or not! When the sun comes up, natural light wakes us up and signals a the start of a new day.

Why did we evolve this way? Simple: We take it for granted now; but in distant past artificial lighting was less safe, more expensive, and much more difficult to maintain. For most of human history, we have traditionally worked and otherwise gone about our lives during daytime hours.

woman looking out window

How Does the Body Respond to Darkness?

When it’s dark, our eyes detect it and the body begins to prepare itself for sleep. The pineal gland in the brain starts producing melatonin, or what is known as the “sleep hormone”. This, in turn, is what makes you feel drowsy.

Melatonin helps relax your muscles, drop your body temperature, and bridge the gap between waking life and dream land. There are other, non-sleep related positive effects, too. For example: It’s been observed to suppress the growth of cancer cells. Melatonin levels pick up as the sun sets, peaking hours after midnight—when we should be asleep—and dropping off as the sun rises.

How Does Technology Affect the Relationship Between Light and Sleep?

The current omnipresence of artificial light has made things difficult.

Electric light fixtures already extend possible waking hours. Put that together with the advent of mass media and digital technology, and the matter gets further complicated. Television, computer, tablet, and smartphone screens also emit artificial light; and they’re not as easy to turn off and set aside.

What’s the harm in using man-made illumination? Turning on the lights, watching TV, and browsing the Internet on your smartphone may seem like harmless luxuries of the modern age; but they are not. More than a few studies over the years have shown otherwise!

Without having to worry about light, people can stay up and out longer—though it’s not always because it’s fun to do so. These days you can party hard well after sunset, but you can also be assigned night shift work. All this contributes to the disruption and degradation of the natural sleep-wake cycle.

The rise of insufficient darkness throughout the night affects the way the body produces melatonin. The pineal gland may suppress or delay the release of melatonin, or end up producing less of it. Artificial light may drown out any natural sleepiness you feel, and replace it with alertness and wakefulness. Sleep disruption of this kind may also affect mood, performance, and even physical health.

More than any other, blue light before bedtime should be avoided. Because it has a short wavelength, it produces a high amount of energy. It’s been observed that long term exposure to blue light causes the most powerful suppression of melatonin production. It can also cause actual physical damage to the human eye!

Bad news for the tech savvy: Blue light is what’s emitted by televisions, computers, and handheld devices.

laptop on bed in dark room

How Do You Manage Light Exposure for Better Sleep?

Artificial light is almost unavoidable. You would need to have total control over your schedule and environment at all times to even attempt to achieve peak sleep-wake efficiency.

The next best thing is to manage your exposure to light to raise sleep quality. You can do this by improving two things: the quality of voluntary light exposure and the darkness of your sleeping environment.

1. Stick to Dimmer & Warmer Artificial Light Hues at Night

Kudos to anyone with enough self-control and restraint to resist using smart devices after sunset! It really is the best thing to do; but barring that, below are some tips to mitigate the harmful effects of artificial light.

You can set the the brightness of your tablet or smartphone screen to the lowest it can go. Many devices also offer an inverted color mode. This helps if you’re reading and want to further decrease brightness by making the screen black and the text white.

There’s also often a night mode that adjusts the color balance; filtering out blue light and making the screen display warmer and less harsh. If you’re on a computer, there are several browser extensions and programs you can run to do the same thing.

You may also consider getting blue light-blocking glasses or using red spectrum light bulbs in your bedroom.

man with face illuminated by smartphone screen in a dark room

2. Keep Your Bedroom as Dark as You Can

Bedroom darkness during the night should be carefully cultivated and preserved. Many products can help with this. If you can’t function in total darkness—which is, after all, understandable—you have a few options.

The goal is to have just enough light for you to see where you’re going and what you’re doing in the hours leading up to bedtime. Ideally, you should sleep in the dark.

Dimmer switches for overhead lights allow you to lower the brightness of indoor lighting gradually through the night. Desk lamps or pin lights you can turn off from your bed are also a good idea. You can also use a night light plugged into an outlet in a secluded corner of the bedroom or in an adjoining closet or bathroom.

If your sleep schedule has you waking up way after the sun rises, you need to manage natural light exposure, too. Heavy blackout curtains over your windows keep out everything from street lights and porch lights to bright sunshine. Even easier: Use a sleep mask! They are a very affordable and effective way to limit light exposure.