Figure 2.

Pattern of light exposure during pre-study period and simulated night shifts: Light intensity data (in lux) was collected via wrist-mounted actigraphy with light sensor during the laboratory and ambulatory segments of the investigation. Irradiance values, approximated for radiation of 400-700 nm from cool-white fluorescent bulbs, are given along the right y-axis. For each individual, data were aligned relative to the end of the sleep/darkness period and averaged into 30-min bins before creating a group mean (shown here as ±SEM). On the lower x-axis, the start of the sleep/darkness episode is assigned a relative clock time of midnight. Light intensity data collected while participants maintained a day-oriented schedule are shown as closed symbols. Light intensity data collected while participants maintained the shifted sleep/wake schedule are shown as open symbols. Data were corrected for use of sunglasses as reported by participants in experimental logs during the ambulatory segment of the study. On the upper x-axis, the initiation of the daytime sleep/darkness episode is assigned a relative clock time of 10:00. The 8-hr sleep/darkness episode is shown as a hatched rectangle.