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.