Figure 2. Relationship between melatonin suppression and circadian phase resetting.

A and B, relationship between light pattern and (A) phase shift, assessed as the difference in circadian phase over 3 circadian cycles between the initial and final constant routines, and (B) melatonin suppression, assessed as the change in AUC over the interval within which the light exposure took place (0.2, 1.0 or 6.5 h, as appropriate) and the corresponding interval which occurred 24 h earlier. For IBL exposures, the entire exposure interval, including the intervening intervals of dim light, was used (e.g. for the 0.2 h condition, AUC was calculated over the entire 1 h interval). Three groups are apparent based on the rank order of the magnitude of phase shift: CTRL < Group 1 (0.2 h, 1.0 h IBL and 1.0 h continuous) < Group 2 (6.5 h IBL and 6.5 h continuous). C, individually matched phase shift and melatonin suppression values plotted for all individuals across the three groups as generated in A; data are shown as means ± SEM.