News Channel Nebraska reports that exposure to light at night — even at very low levels — has been linked to an increased risk of depression, according to a study published this month in the American Journal of Epidemiology.

In general, nighttime light has been shown to disrupt internal sleep/wake cycles, which is an ever-growing concern as more people are using their phones and tablets in bed or leaving the TV on as they sleep.

But the new report goes further, measuring bedroom exposure to low levels of nighttime light using a portable light meter attached to the bed. Researchers followed nearly 900 elderly people in Japan for two years, assessed symptoms of depression and tested sleep/wake patterns throughout the night. They took into account weight, smoking or drinking habits; income level; and medication use. Histories of high blood pressure, diabetes and physical activity level were also noted.