This study, run by the Harvard School of Public Health, indicated that children lose seven minutes of sleep for every hour of television they watch a day. They followed 18,000 children aged 6 months to nearly eight years. Children under eight who had a television in their room were less likely to get the right amount of sleep and lost an average of 30 minutes of sleep a night. Sleep deprivation is linked to poor performance at school and to depression, injury and obesity. Current NHS advice suggests that televisions should be kept out of bedrooms to encourage sleep.

http://www.thecrimson.com/article/2014/4/15/study-television-sleep-HMS