RecruitingPhase 4Device studyLight Flashes to Treat Delayed Sleep Phase Disorder (DSPD)Delayed Sleep Phase Disorder (DSPD) is a sleep disruption that commonly occurs in teens and manifests as a difficulty in waking up in the morning, going to sleep early enough at night, and daytime disturbances such as depression, fatigue, and restlessness. The purpose of this study is to determine if brief flashes of light, that are scheduled to occur during sleep, are effective in treating DSPD.