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

The timing and quality of sleep is governed by environmental and physiologic factors. Environmental factors, especially ambient lighting can impact the circadian system and alter the timing and structure of sleep. Light exposure can also acutely alter neural activation state and impair sleep. These effects all demonstrate marked sensitivity to short-wavelength blue light with maximal sensitivity in the 460-480 nm range. The alerting effects of blue light in the evening persist for at least 3-4 hours after the lights are turned off, and can disturb subsequent sleep. Avoiding these deleterious effects of light exposure prior to sleep on subsequent sleep would be beneficial to sleep quality and potentially health.

The investigators will compare the effects of two light sources, equated for visual stimulus (lux), on multiple non-visual responses to light. The investigators will compare a 90 lux exposure of a commercially available Compact Fluorescent Light (CFL) with a novel LED white light source that is depleted in the short-wavelength visible range (Biological Illumination LCC, FL). In a within-subject design, the investigators will test the hypotheses that exposure to a blue-depleted LED as compared to a CFL exposure at (1) 90 lux or (2) 50 lux will cause significantly:

1. Less melatonin suppression between melatonin onset and bedtime;
2. Less subjective and objective alerting responses before bedtime;
3. Less disruption of nocturnal sleep structure and quality.


Eligibility Criteria:
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.