Why Sleeping With the Lights On May Affect Your Health

You may not think much about the amount of light in your bedroom when you’re sleeping, but a recent study shows that a healthy sleep environment might be one with little to no light. From a TV screen emitting a soft glow to a street light that slips through the blinds, your body may be paying more attention to nighttime light exposure than you would think.

New research from Tulane University has added to growing evidence that nighttime light exposure may affect more than just how easily you fall asleep. In a study of more than 11,000 people, researchers found that people exposed to higher levels of light at night had measurable differences in the structure and function of their hearts several years later. The findings don't prove that bedroom light causes heart disease, but they add another reason to take the darkness of your sleeping environment seriously.

Your Body Doesn't Treat Nighttime Light Like A Neutral Background

Light is one of the most important signals that your body uses to determine when you should sleep and when you need to be awake. Light exposure during sleep can send mixed signals to your brain, telling your body that it’s time to wake up, even when it’s not.

The body’s circadian rhythm operates on a 24-hour cycle, and your eyes processing light helps regulate those rhythms. As evening arrives and the sun stops beaming through your windows, your brain starts producing more melatonin, a hormone that regulates sleep timing. Artificial light can interfere with that pattern, even while your eyes are closed. That doesn't mean every bit of light in your bedroom is going to ruin your sleep, but the timing, brightness, and color of the light can all matter.

A New Study Looked At What Happens Inside The Heart

There have been plenty of studies conducted about bedroom light and sleep, but most of those focused only on sleep quality. The latest research goes beyond that. Published in the European Heart Journal in September 2026, the study examined 11,071 participants from the UK Biobank who wore wrist devices containing light sensors for seven days. Researchers then used cardiovascular magnetic resonance imaging three years later to examine their hearts.

According to the findings, participants who were exposed to more than three lux of light had evidence of changes in cardiac structure and function compared to those with minimal to no nighttime light exposure. Specifically, the research team found greater left ventricular mass and wall thickness, along with a reduction in myocardial contraction fraction, a measure related to how effectively the heart contracts.

It’s important to note that three lux of light is not particularly bright. According to the researchers from Tulane, it’s roughly the same amount of light that’s emitted from a cellphone set on low brightness and sitting on a nightstand. The researchers weren't studying people sleeping under stadium lights. They were examining relatively ordinary nighttime exposure.

The Study Does Not Prove That A Nightlight Causes Heart Disease

Researchers were careful about explaining that they’re not claiming that nighttime light exposure causes heart disease. The study found an association between nighttime light exposure and changes in the heart. It did not establish that turning on a nightlight causes heart failure, atrial fibrillation, or a heart attack.

While they don’t provide a direct correlation between light exposure and heart problems, the findings are notable because they fit into a larger body of research pointing in the same general direction. The Tulane researchers found that shorter sleep duration statistically mediated some of the relationship between nighttime light exposure and cardiac changes, providing one possible explanation for how the two could be connected.

Earlier Research Found Immediate Effects From Brighter Light

The latest study from Tulane didn’t happen in isolation. In 2022, a research team from Northwestern Medicine studied a group of adults who spent a single night sleeping under moderate room lighting of 100 lux compared to very dim lighting of roughly three lux. Participants exposed to moderate light experienced higher heart rates and greater sympathetic nervous system activation during sleep. They also showed increased insulin resistance the following morning.

There’s no guarantee that sleeping with the lights on is going to cause cardiac issues, but the study does show some potential connections between the two. The latest study serves as a powerful reminder that sleep quality plays a pivotal role in overall health and wellness.

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