1. Fig. 2. Plasma melatonin secretion profiles for each of the eight subjects across the three conditions in the study. Profiles are shown for the entire 40-h constant routine (CR), with the 6.5-h light exposure (LE) demarcated on each. Shading indicates dim (∼0.5 lux) lighting conditions. Plasma melatonin secretion is reported in picomoles per liter. A, Baseline plasma melatonin profiles in dim light (∼0.5 lux). B, Plasma melatonin profiles during the approximately 200-lux CR with a 200-lux LE. Note the diminished amplitude in most subjects and the delayed melatonin secretion onset. C, Plasma melatonin profiles during the approximately 0.5-lux CR with a 200-lux LE. Note the markedly depressed melatonin amplitude during the light exposure followed by resumed melatonin secretion and the delay in melatonin onset in most subjects.
From: Adaptation of Human Pineal Melatonin Suppression by Recent Photic History
J Clin Endocrinol Metab. 2004;89(7): doi: /jc
J Clin Endocrinol Metab | Copyright © 2004 by The Endocrine Society

2. Fig. 1. The protocol is presented as a standard double raster plot, with consecutive days plotted side by side. The order of d 6–9 and 10–13 was reversed for half of the subjects. Black shaded bars represent sleep episodes (0 lux). Open bars represent an ambient light level of approximately 200 lux at the angle of gaze. Each constant routine (CR) lasted 40 h. Sun icons represent light exposure periods of 6.5 h each centered at 18 h 10 min after habitual wake time. After 3 baseline days, subjects underwent an initial CR and light exposure entirely at approximately 0.5 lux for assessment of baseline melatonin secretion. Each subject then underwent 2 baseline days of either approximately 0.5 or 200 lux, after which they again underwent a CR at the same light level with a 200-lux (angle of gaze) light exposure, to examine differences in the melatonin profile during the 200-lux light exposure between the two lighting histories as well as before and after the light exposure.
From: Adaptation of Human Pineal Melatonin Suppression by Recent Photic History
J Clin Endocrinol Metab. 2004;89(7): doi: /jc
J Clin Endocrinol Metab | Copyright © 2004 by The Endocrine Society