Figure 3. Fitted and normalized curves to the melatonin profiles of one subject.

The profiles with the dashed lines are from the baseline phase assessments and the profiles with the continuous lines are from the final phase assessments. The horizontal lines at 25% are the thresholds for determining the dim light melatonin onset (DLMO) of each curve. A, lab session without blue light. The DLMO delayed 3.0 h due to the free-run through the ultradian LD cycle. B, lab session in which intermittent blue light was applied once a day during the 3 days of ultradian LD cycles. The shaded rectangle over the x-axis shows the time of the blue light stimulus. The DLMO delayed 1.5 h. Thus, the net phase shift due to the blue light alone, after subtracting out the delay from the free-run, was an advance of 1.5 h.