While screen time has already been proven to negatively affect the sleep patterns of both adults and kids, a new study of more than 6,600 adolescents shows that kids who use their smartphones, e-readers, or watch TV in darkened rooms actually sleep even worse.

Researchers from Imperial College London, the University of Lincoln, and London's Birkbeck University, along with the Switzerland's Tropical and Public Health Institute found that more than 71% of children polled admitted using a screen before bed, and 32.2% did so when their bedroom lights are off.

The findings, published in the journal Environment International, noted that while using any screens before bed with the lights on caused 31% of those kids polled to get less sleep than those who didn't have any pre-bed screen time.

However, the new study showed that those who used screens with the lights off were 147% more likely to get less sleep than the screen-free kids.

The study's lead author, Dr. Michael Mireku, explained, "While previous research has shown a link between screen use and the quality and length of young people's sleep, ours is the first study to show how room lighting can further influence this."