Two treatment modalities will be evaluated alone and in combination: 1) light-induced suppression of daytime melatonin release and delay of nighttime sleep; and 2) pharmacological replacement of nocturnal melatonin. Melatonin levels measured in blood (Pre- vs. Post-treatment) will serve as the primary outcome parameter. A dTR-melatonin tablet developed by the Clinical Center Pharmaceutical Development Services (CC-PDS) will be used in this trial.