Investigating the Effects of Evening Light Exposure on Melatonin Suppression, Alertness and Nocturnal Sleep

Inclusion Criteria: (i) Aged between 18-30 years to reduce the confounding effects of lens aging on the transmission of light to the retina; (ii) Non-smoking for at least 6 months; (iii) Healthy (no medical, psychiatric or sleep disorders); (iv) No clinically significant deviations from normal in medical history, vital signs, physical examination, blood chemistry and hematology, urine chemistry and ECG; (v) Women of childbearing potential must agree to use an acceptable method of birth control, and must have a negative urine pregnancy test; (vi) Body mass index of \> 18 or \< 30 kg/m2; (vii) No drugs or medication likely to affect sleep or alertness, as determined by the investigators; (viii) Habitual caffeine consumption \< 300mg per day on average; (ix) Habitual alcohol consumption \< 10 alcoholic units per week on average. Exclusion Criteria: (i) History of alcohol or substance abuse; (ii) Positive result on drugs of abuse screening; (iii) Current or past history of sleep disorders, including but not limited to obstructive sleep apnea, or any significant sleep complaint; (iv) Psychiatric disorder; (v) Recent acute or chronic medical disorder, including but not limited to hepatic impairment and severe chronic obstructive pulmonary disease; (vi) Visual disorder, including but not limited to color blindness, or family history of glaucoma; (vii) History of intolerance or hypersensitivity to melatonin or melatonin agonists; (viii) Pregnancy or lactation; (ix) Shift work; (x) Transmeridian travel (2 or more time zones) in past 2 months; (xi) Any other reason as determined by the Principal Investigator.