Leaving your bedroom lights on while you sleep may lead to a higher risk of heart disease, a new study has found. Research from Tulane University found that people who slept with more light in their rooms went on to develop a 29% higher risk of heart failure than those who slept in total darkness. The study involved more than 70,000 adults, and measured light exposure at night using wrist-worn sensors. Researchers then scanned participants' hearts with MRI three years later, finding that those with the most nighttime light had thicker heart walls and larger heart chambers. Follow-up health records from participants also showed higher rates of heart attack, irregular heartbeat, and death from heart disease. This is the first study to connect nighttime light exposure to physical changes inside the heart, rather than just blood pressure or cholesterol numbers. The research suggests that exposure to light while you sleep may not just be an annoyance, but a genuine risk factor when it comes to your cardiovascular health.