Circadian rhythm disorders are disruptions in an individual's circadian rhythm, or "internal body clock." This internal clock regulates the 24-hour cycle of biological processes in the body, including sleep and hormone production. Jet lag, delayed sleep phase syndrome, in which individuals fall asleep and wake up later than desired, and advanced sleep phase syndrome, in which individuals fall asleep and wake up earlier than desired, are all examples of circadian rhythm disorders. Because of the disruptive nature of these conditions, it is important to identify the quickest and most effective method for regulating the body and reestablishing normal sleep patterns. Light therapy, in which individuals are exposed to bright, artificial light, is currently used to treat these disorders. Melatonin, a hormone that regulates circadian rhythms, and methylxanthines, a class of stimulant medications, are other common non-light treatments. While each of these individual treatments has been proven effective, little is known about the combined effect of light and non-light treatments. The purpose of this study is to evaluate the safety and effectiveness of light therapy, melatonin, and methylxanthine, alone and in combination, at regulating circadian rhythms and improving sleep quality and cognitive function.