Participants Participants were between the ages of 20 and 45 years, with BMI 18-25, regular sleep habits in Pittsburgh Sleep Quality Index (PSQI) questionnaire index<5 (Buysse et al., 1989, Shochat et al., 2007), and a normative sleep-wake cycle type (Horne-Ostberg morningness-eveningness questionnaire (Horne & Ostberg, 1976, Lavie & Segal, 1990) measured Sleep quality and continuity were measured for one week using actigraphy with compatible decoding software (Respironics Model II, Philips, Inc). Only participants with 6-8 hours of sleep, normative sleep patterns, and no sleep/wake schedule problems proceeded to the experimental phase of the study stage. Participants were healthy with no history of medical, neurological, sleep disorders (confirmed by polysomnography) or psychiatric conditions and no medication intake (excluding contraceptives for female participants). Participants with ocular damage, such as to their field of vision, color blindness, or impaired functioning of the pupil in reaction to light were excluded, however use of eyeglasses or contact lenses to correct vision was allowed. Participants signed informed consent prior to participation in the study. The study was approved by the Helsinki Committee of Assuta Medical Center and Maccabi Health Services.