 On the base-line, first and fifth night of the study, at the end of two hours of exposure to screen light, the subject will be connected to the sleep test system by a skilled technician. On all other nights nights 2-4, exposure to computer light only, will be conducted and at the end of the exposure the subject will be asked to go to sleep. During the entire experimental period the subject will wear an Actigraph watch to ensure regular sleeping hours. In addition, subjects will be asked not to expose themselves to a computertabletsmartphone screen from 20:00 h to wake up. 