A new study from the Uni Research Health in Bergen, Norway has confirmed that the cumulative amount of screen time a teen gets throughout the day will directly effect both the onset of sleep and its duration. In particular, teens who used a computer or mobile phone in the last hour were 52% and 48% likelier to take more than 60 minutes to fall asleep. They were also 53% and 35% likelier to lose out on two or more hours of sleep.
http://blogs.bmj.com/bmjopen/2015/02/02/cumulative-daily-screen-time-linked-to-teen-sleep-problems/
http://www.livescience.com/49670-teenage-sleep-screen-time.html
http://www.reuters.com/article/2015/02/03/us-teen-sleep-screen-time-idUSKBN0L72F420150203
ALSO
How to talk to your teens about the amount of sleep that they need by discussing consequences that are relevant to them:
http://health.heraldtribune.com/2015/02/03/persuading-teenagers-sleep-nine-hours/
