Each of us has a biological clock that regulates our circadian rhythms, including the times we sleep and are awake. Light is the most important factor that helps determine when we should feel awake (usually during the day) and when we should feel sleepy (usually at night).

So, let me ask you a personal question: How dark is your bedroom? To find out why this is important and whether you should sleep with an eye mask on, read on.

What Does Light Have to Do with Sleep?

Our circadian system evolved before the advent of artificial light. Light with just a few watts of power can trick the brain into thinking it’s daytime at any time of the night. So, what keeps your bedroom lit?

A tablet watching a movie while lying in bed at night is over 100 times brighter than watching a movie outdoors during a full moon. Working in front of or looking at a computer screen at night is approximately 10 times brighter than standing in a well-lit parking lot.

Light exposure at night affects the natural processes that help the body prepare for sleep. Specifically, your pineal gland secretes melatonin in response to darkness. This hormone is integral to the circadian regulation of sleep.

What Happens When We Are Exposed to Light at Night?

Exposure to light at night inhibits the production of melatonin, which changes our sleep patterns. Adults who slept next to a nightlight slept for shorter periods of time and woke up more frequently than those who slept without it. Even outdoor artificial light at night, such as street lights, has been linked to less sleep.

But the effects of nighttime light aren’t limited to sleep. It also increases the risk of depressive symptoms, obesity, diabetes and high blood pressure. Lighting is inconsistent with our circadian rhythm, which means it’s dark during the day and bright at night, which is one reason scientists believe shift work puts people at greater risk for serious health problems.

Would Sleeping with an Eye Mask Help?

Researchers at Cardiff University in the UK conducted a series of experiments to examine whether wearing eye masks while sleeping at night could improve certain measures of learning and alertness. Approximately 90 healthy young adults aged 18 to 35 alternately slept with an eye patch or exposed to light at night. They recorded their sleep patterns in sleep diaries.

During the first part of the study, participants wore the eye patches intact for a week. Then for the next week, they wore an eye patch with a hole exposed for each eye so the patch didn’t block light.

After sleeping with no light exposure (wearing an intact eye patch) and minimal light exposure (wearing an eye patch with holes), participants completed three cognitive tasks on the sixth and seventh days of the week :

The first is the paired learning task. This helps show how efficiently a person learns new associations. The task here is to learn related word pairs. Participants who wore full eye masks while sleeping for several days before the test performed better than those who were exposed to lights at night.

Second, the researchers administered a psychomotor alertness test to assess alertness. Blocking out light at night also improves reaction times on this task.

Finally, a motor skill learning test was administered that consisted of tapping a five-digit sequence in the correct order. There was no difference in performance on this task whether participants wore full eye patches or were exposed to light at night.

What Else Did the Researchers Discover?

No study is perfect, so it’s important to take the conclusions above with a grain of salt. According to sleep diary data, there were no differences in how long people slept or in their perceptions of sleep quality whether they wore eye masks or not.

Additionally, in a second experiment with 30 participants, researchers tracked sleep objectively. They found that there were no changes in sleep architecture, such as the amount of time participants spent in REM sleep when wearing eye masks.

Should I rush out and buy an eye patch before an important meeting or exam? If you decide to try an eye patch, there may be no extra cost. Instead, follow the chronobiologist’s rule of thumb: “Bright during the day, dark at night.”