Inclusion Criteria:  Healthy adults with conventional and regular sleep-wake timing Non-smokers Completion of medical, psychological, and sleep screening tests Able to spend 33 consecutive days/nights in the laboratory Normal color vision  Exclusion Criteria:  History of neurological or psychiatric disorder History of sleep disorder or regular use of sleep-promoting medication Current prescription, herbal, or over-the-counter medication use Traveling across 2 or more time zones within past 3 months Donating blood within past 8 weeks Worked night or rotating shift work within past 3 years Hearing impairment, visual impairment History of eye trauma or surgery Drug or alcohol dependency