Figure 4. Melatonin levels and pupillary constriction during nocturnal light exposure.

(A) Melatonin profiles are shown for participants exposed to 6 h of continuous red light (left), intermittent red light and darkness (center), or bright white light (right) near the onset of melatonin secretion. Black traces show the melatonin rhythm on the day prior to light exposure, and gray traces show melatonin on the day of the light exposure session. Melatonin concentrations during light exposure were individually adjusted using Z-score values obtained during the first constant routine procedure. Vertical dotted lines indicate the onset and offset of the light exposure session. (B) The area under the curve (AUC) of the melatonin profile during light exposure is shown for each subject, expressed as a percentage of his AUC measured in dim light. Values less than 100% therefore indicate light-induced melatonin suppression, whereas values that exceed 100% indicate that the AUC was higher during the light exposure session relative to the AUC measured in dim light on the previous day. The open circles show responses for subjects crl30 and irl31, who exhibited substantial resetting of circadian rhythms, as shown in Figure 3. (C) The pupillary light reflex is shown during the first 50 min of exposure to continuous red light (left), alternating red light and darkness (center), and bright white light (right). (D) The median pupillary light response is shown for individual subjects during the 50-min fixed gaze period, expressed relative to the dark pupil. Horizontal dotted lines in C and D indicate pupil diameter in darkness, and data in C are binned at intervals of 15.625 s, corresponding to one-quarter of an intermittent lights-on pulse. In A and C, the mean ± SEM is shown. In B and D: crl, continuous red light; irl, intermittent red light; bwl, bright white light.