We are looking for healthy men and women, ages 18-45, to participate in a study lasting approximately 15 days. The study will consist of wearing an activity-tracking watch at home, and two laboratory visits of about seven hours each at the University of Colorado Boulder Sleep and Chronobiology Laboratory. This study is about how typical artificial indoor lighting versus a simulation of a natural sunset influences the timing of the human body clock. The body clock controls 24-hour patterns of physiology such as sleep and hormone release. This work will have important implications for determining how implementation of new lighting technology can be used to promote sleep. Participants may receive compensation up to $200. For study details, email sleep.study@colorado.edu and ask about the Simulated Sunset study.