Figure 1. A raster plot of the experimental protocol for subject 1843.

Consecutive days are plotted from top to bottom. Clock time is indicated on the horizontal axis. The protocol began with three 24 h baseline days on the subject's habitual sleep–wake schedule with 16 h wake episodes in < 150 lx illumination (□) and 8 h sleep opportunities in darkness (▪). A pre-stimulus CR in dim light (< 15 lx, ▪) began on day 4 and continued until the 8 h sleep episode on day 5. The light exposure day consisted of 16 h of ambulatory wakefulness in dim light, interrupted by a seated 6.7 h bright light exposure (∼10 000 lx fixed gaze, □) centred in the middle of the wake episode. A subsequent 8 h scheduled sleep episode was followed by a post-stimulus CR and a recovery sleep episode. The timing of the melatonin midpoints for evaluation of the phase shift is indicated by ▵. For this subject, the light exposure generated a phase delay of −3.60 h in the melatonin midpoint._.