Your Bedroom Probably Isn’t Dark Enough

Every day, as sunlight streams into your eyes, trillions of tiny clocks in your cells reset. The human body uses light to correctly time myriad processes, ensuring that liver enzymes are made on schedule, hair cells divide at the right time, and blood pressure stays at a healthy level. People who don’t get their daily dose of light at the right time of day can end up with worse health.

But for all its usefulness, researchers are increasingly realizing that light has a dark side. In 2019...