Darkness is not just a preference.
It is part of how your body prepares for sleep.

Research in chronobiology, neuroscience, and sleep medicine connects light and environmental distractions with sleep disruption. The science breaks down into four simple ideas.

#1 The light-melatonin suppression pathway

Light tells your brain, “stay awake,” even when your body needs rest.

Melatonin is the hormone that helps signal darkness and prepares the body for sleep. When light hits the retina, it sends a signal to the brain’s master clock, the suprachiasmatic nucleus. Evening light can suppress melatonin and delay the body’s natural transition into sleep.

Read the room light and melatonin study | Learn more on how light affects sleep

#2 Artificial Light at Night and Sleep Architecture (ALAN)

You may fall asleep, but light can still affect the quality of your sleep.

Light can affect sleep even after you fall asleep. Artificial light at night may disrupt how the brain moves through sleep stages, making sleep lighter, more fragmented, and less restorative.

Read about artificial light at night and sleep quality | Read the NIH-AARP light at night study

#3 The blue light and digital distraction multiplier

Screens do not just add light. They add stimulation.

Phones, tablets, laptops, and TVs can disrupt sleep in two ways. They expose your eyes to light, especially short-wavelength blue light, and they keep your mind engaged when your body should be winding down.

Read about light at night and sleep | Read about good light, bad light, and better sleep | Learn about light and sleep environment

#4 The power of absolute darkness, the natural baseline

Your body works best when daytime is bright and nighttime is dark.

To understand sleep, researchers often look at environments with natural daylight and true darkness at night. When people spend time away from artificial light and digital distractions, their sleep timing and melatonin rhythms can shift closer to the natural solar cycle.

Read about the natural light-dark cycle

Your sleep space may be brighter than you think.

Light does not only come from windows. It can come from phones, TVs, chargers, clocks, door gaps, bathroom lights, nightlights, partner screens, and early morning sun.

"It’s important for people to avoid or minimize the amount of light exposure during sleep."

Phyllis Zee, MD, PhD, Northwestern Medicine | Northwestern Medicine Healthbeat article

Sources

Sleep Foundation: Sleep Hygiene
https://www.sleepfoundation.org/sleep-hygiene

Sleep Foundation: Light and Sleep
https://www.sleepfoundation.org/bedroom-environment/light-and-sleep

Journal of Clinical Endocrinology & Metabolism: Exposure to Room Light Before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans
https://pmc.ncbi.nlm.nih.gov/articles/PMC3047226/

Chronobiology in Medicine: Artificial Light at Night and Sleep Quality
https://www.chronobiologyinmedicine.org/journal/view.php?number=165

NIH-AARP Diet and Health Study: Outdoor Artificial Light at Night and Short Sleep Duration
https://pmc.ncbi.nlm.nih.gov/articles/PMC6996197/

Cleveland Clinic: Can Light at Night Interfere With Sleep?
https://health.clevelandclinic.org/light-night-can-interfere-sleep

National Sleep Foundation: Good Light, Bad Light, and Better Sleep
https://www.thensf.org/good-light-bad-light-and-better-sleep/

UCLA Health: Artificial Light Interrupts Circadian Cycle
https://www.uclahealth.org/news/article/artificial-light-interrupts-circadian-cycle

The Washington Post: A Doctor’s View on Melatonin
https://www.washingtonpost.com/health/2026/06/21/risks-rewards-melatonin-doctor-view/