Figure 2. Winter Circadian and Sleep Timing.

Average timing of melatonin onset (black upward triangles), midpoint (red squares), and offset (blue downward triangles) following one week exposure to electrical and natural lighting in the modern environment versus following one week exposure to only natural light while camping. Average sunrise and sunset times for the ~2 week study are denoted by vertical black lines. Average sleep start and end times are indicated by the black bar for each week. Clock time = local time. Data are represented as mean ± SD. See also Figures S1–S3.