Figure 1. Light Exposure Relative to Clock Time (20:00-05:00 h).

The y-axes depict hourly average lux values on a logarithmic scale. Outcomes were transformed to the log(lux+1) scale to better approximate model assumptions and to bound values away from 0 (or logged values away from negative infinity). The x-axes depict hourly time intervals. Clock times correlate with an hourly interval that begins at the corresponding time and ends 1-hour later (e.g., the 0400 data point corresponds to the lux interval encompassing 0400-0500 h). In the figures that describe time in relation to the time of sleep onset or offset, the intervals 0-8 are calculated in an identical fashion. The intervals -1 to -8 encompass the preceding hour (e.g. interval -8 refers to the lux recorded between 7 and 8 hours prior to sleep onset or offset. The rectangles encapsulate the illuminance intervals of interest. Asterisks denote hours during which statistically significant group differences were identified (regardless of school night/morning status), with affiliated p-values. Circles represent DSPD-A subjects (cases), and squares controls. Open and closed shapes are representative of school night and non-school night status, respectively.