Figure 4

Activity and light exposure graphs: Nurses. Activity and light exposure data plotted as a function of elapsed number of days for a day-shift nurse (4a, 4c) and for a rotating-shift nurse (4b, 4d). Data collection started at a different clock time for each subject, so each "day" is a different 24-hour period of time for each subject. Circadian light stimulus (CS) exposures were measured with the Daysimeter [20], and transformed to range between the limits of human melatonin suppression (CS Logistic) shown in Figure 3.