A Japanese study warns that turning on the night lights while sleeping increases the risk of fatal illnesses, and even the light from a street lamp or moon can cause harm.
Leaving light in the room while sleeping increases the risk of death from heart disease and stroke, the researchers said.
Doctors also found that even low levels of night light leaking into the bedroom from the moon or street lamp might be enough to cause damage, and researchers found that higher levels of light pollution were offset by higher rates of atherosclerosis.
According to the researchers, exposure of the eyelids to light during sleep reduces the production of hormone melatonin in the body during the night, which helps to sleep for longer hours, and works to reduce blood pressure and glucose levels and body temperature during sleep.
"We found a clear correlation between sleep in light and atherosclerosis, which is independent of known causes such as smoking, obesity, hypertension and diabetes," study lead author Kenji Obiashi said.