One of our goals at Nightside is to create a better sleeping environment for those who want a more gradual transition between wakefulness and sleep. It's the reason we designed our NS01 task light to be completely dark when turned off, with no status or power lights that stay on in the darkness. The result is a darker bedroom when you turn out the lights.
Recently we came across a very interesting article in the December 2025 issue of Time Magazine that encapsulated the following study linking ambient bedroom light with sleep and overall cardiovascular health. Findings like those in this study increasingly reaffirm the importance of our mission.
Here is a summary of the article:
Your Bedroom Probably Isn't Dark Enough
by Veronique Greenwood
"Modern electric lighting and screens have made evenings and bedrooms brighter than at any time in human history — and that may be harming our health, particularly our hearts.
A large new study of nearly 90,000 adults has linked nighttime light exposure during sleep with higher long-term risk of cardiovascular disease, including heart attack, atrial fibrillation, heart failure, and stroke. These associations remained even after researchers adjusted for traditional risk factors such as body weight, diabetes, and sleep duration.
How the Study Worked
Researchers used data from the UK Biobank, which included light exposure readings from fitness trackers worn on participants’ wrists. These devices recorded ambient light levels throughout the day and night. For nighttime exposure, researchers focused on readings between midnight and 6 a.m. Participants were grouped by how much light their devices picked up during those hours.
Roughly half the participants experienced very low levels of light at night — essentially near darkness — while others had increasingly brighter environments. Even fairly modest exposure (about 100 lux, roughly the level of a dim hotel hallway) was enough to define the top decile of light exposure.
Key Findings
- Higher Light = Higher Risk: People with brighter nighttime environments were significantly more likely to develop heart disease over the next decade than those with darker nights. The risk increased consistently with brighter exposure.
- Independent of Sleep Duration: The link between light exposure and heart problems persisted even after accounting for how long people slept, indicating that the effect isn’t just about getting less sleep.
- Beyond Standard Risk Factors: Even after adjusting for common cardiovascular risk factors like body mass index and prediabetes, light exposure remained a strong predictor of disease, suggesting it has its own biological impact.
- Consistent with Other Research: Previous smaller studies have found related links between light at night and conditions like obesity, diabetes, hypertension, and metabolic disruption.
Possible Mechanisms
Researchers believe the effect stems from circadian rhythm disruption — the internal body clock that tells us when to sleep and wake, and that helps regulate hormones, metabolism, blood pressure, and many other physiological processes. Light is the main cue for synchronizing this clock, so unnatural light at night can throw the system off.
One possible mechanism involves melatonin suppression. Darkness signals melatonin production, which helps signal night and healthy sleep cycles. Light exposure can delay or stop melatonin release, keeping the nervous system in a more alert state and possibly elevating heart rate and metabolic activity when the body should be resting.
Lab studies supporting this idea have shown that even one night of moderate light exposure (around the same level seen in many bedrooms) can cause heart rates to remain elevated during sleep and affect insulin metabolism the next day.
Implications & Takeaways
The findings suggest that light exposure at night is a modifiable risk factor for cardiovascular disease, and that simple changes — such as reducing light in the bedroom, using blackout curtains, turning off TVs and bright devices before bed, and keeping ambient lights dim or off — could support heart health.
While the study cannot definitively prove causation, it adds to a growing body of evidence that a dark sleeping environment matters not just for sleep quality, but for long-term health outcomes as well."
