Figure 2.

Changes in melatonin levels during night shifts with exposure to visual short-wavelength-filtered light and standard ambient artificial light. Melatonin levels were significantly higher under intervention (exposure to short-wavelength [<480 nm]-filtered light during night shifts) as compared with baseline (exposure to standard unfiltered ambient light during night shifts) on the first night shift (A) and middle night shift of a series of three consecutive night shifts (B). Individual profiles are presented as gray lines and group mean ± SEM profiles are presented as blue lines. Mean melatonin profiles are compared between the two conditions and two nights of testing (C). Data were subjected to two-factor (group × time) mixed-model ANOVA for the first and fourth night shifts individually. Statistically significant values at specific times as revealed by post hoc analysis are represented by *. Percentage change in melatonin AUC between baseline and intervention conditions on the first and second nights were calculated to assess changes in melatonin levels on an individual basis (D). Group mean ± SEM for each night is expressed as the bars and individual levels are expressed as gray filled circles. The change in AUC was significantly greater on the fourth night as compared with the first night.