Are you ages 18-45 and healthy? This study is about how artificial indoor lighting influences the timing of the human body clock compared to an indoor simulation of a natural sunset. This work will have important implications for determining how new lighting technology can be used to promote sleep. Looking for participation in a study lasting 15 days consisting of wearing an activity tracking watch at home and two laboratory visits of about seven hours each at the CU Boulder Sleep and Chronobiology Laboratory. Compensation up to $200. For study details, email sleep.study@colorado.edu and ask about the Simulated Sunset study.