Conventional wisdom has long held that parents should not allow children to have a television in their bedroom. The detrimental effects of watching too much TV are well documented. But in this day and age, how many young people are still watching TV? What about all of the smartphones and tablets and video games?

In a new study published in the BMJ Open, Norwegian researchers surveyed a wide swath of teenagers between the ages of 17 and 19. Almost 10,000 adolescents were questioned about their screen habits across multiple platforms throughout the day, including right before bedtime. They were then asked how long it took to fall asleep each night and how refreshed they felt the next morning. Researchers then divided the respondents into two categories depending on whether they could fall asleep in less than an hour or if it took them longer to fall asleep. Based on this distinction, the scientists examined the screen time of the teenagers.

While the researchers expected to see a correlation between poor sleep and screen time, the degree was shocking. When the amount of time in front of any screen was greater than four hours, adolescents had a 50 percent greater risk of having difficulty falling asleep. And the more hours any teen spent plugged in, the more disturbed their sleep became. Teenagers who spent over four hours in front of a screen throughout the day typically got less than five hours of sleep each night.

On average, boys spent about six and a half hours a day in front of a screen, typically playing video games. Girls reported slightly less time in front of a screen, approximately five and a half hours a day, watching TV or chatting online with friends.

Prior research held that spending more time in front of a screen meant less time to spend sleeping. However, new research suggests that screen time interferes with sleepiness. The study’s authors suggest that staring at an illuminated screen for extended periods of time, in particular before bedtime, disrupts the body’s natural clock. Increased screen time could be keeping adolescents and adults alert when they should be feeling drowsy. More research needs to be done to draw any concrete conclusions. However, the researchers suggest parents limit the time children spend in front of any and all screens, not just televisions.