Passive phototherapy to improve sleep in teens - It is a nearly ubiquitous phenomenon – teens have a difficult time going to sleep early enough to get a full night of sleep. The resulting sleep curtailment is associated with a variety of negative consequences including depression, substance abuse, fatigue, poor academic or work performance, poor socialization, increased risk-taking behavior, and an increased risk for the development of diabetes and obesity. According to the Department of Health and Human Services in Healthy People 2020, fewer than one-third of all students in grades 9-12 get sufficient sleep – a number that has remained unchanged since 2009. This pervasive loss of sleep in adolescence is often debilitating for both the teen and the family. There are both biological (natural delay in circadian timing) and social causes, which are mutually reinforcing, for this delay in sleep timing. As a treatment for the biological component, bright light “phototherapy” is often prescribed for teens who wish to go to sleep earlier. This treatment often consists of 1-2 hours of bright light administered every day prior to desired wake time; this treatment is meant to advance the timing of the circadian clock to an earlier hour. This means that an adolescent who needs to wake up at 7AM for school would need instead to wake up at 5 or 6 AM and sit in front of bright lights for hours every day (the changes in circadian timing would revert without the daily light exposure), a difficult if not impossible set of instructions to follow. We have recently demonstrated that: (1) sequences of brief, millisecond light flashes are more potent than continuous light at changing the timing of the circadian clock, (2) exposure to such sequences of light during sleep impacts circadian timing without significantly interfering with sleep, and (3) at-home exposure to such sequences to teens increases self-reported nightly sleep by nearly one-hour per night. We hypothesize that such a light sequence can increase objective measures of sleep length, as well as improve mood and cognition in teens. In order to examine these hypotheses, adolescents enrolled full-time in high school will be recruited to take part in a 10-week, at-home placebo-controlled parallel group study, followed by a 10-week open-label study. For 8 of the 10 weeks of the parallel group study and during all 10 weeks of the open-label study, adolescents will be exposed to a sequence of flashes while they sleep. The quality and quantity of their objectively-determined sleep, measurements of mood from both the adolescent’s and the parent’s perspectives, and executive function, will be captured before, during, and at the end of the protocol. Results from this experiment could fundamentally change the manner in which delayed sleep is treated, significantly improving sleep in adolescents and simultaneously improving mood, academic performance, and family life. Results from this study will also be useful in understanding how light administration during sleep could be useful in the treatment of circadian-based sleep disorders, such as jet lag, shift work sleep disorder, and Advanced Sleep Wake Phase Disorder.