Figure 1.

Schematic representation of study protocol and spectral transmission profile of filtered light. Nine full-time nurses participated in the 8-wk study (A). Each participant completed 8 wks consisting of 2-wk rotation periods of alternating night and day shifts (gray bars). Working days were separated by two to three non-workdays (white bars). Participants were randomized in a crossover design (marked by X) to receive glasses fitted with short-wavelength filters (0% transmission <480 nm) to be used only during night shifts (intervention) or exposed to regular unfiltered ambient artificial light (baseline). Sleep and alertness under baseline and intervention conditions (red hashed bar and red filled circles) were compared with nighttime sleep after the seventh day shift (polysomography) and alertness measures taken during the seventh day shift on the second 2-wk day shift period (comparator; blue hashed bar and blue filled circles). Baseline and intervention for nighttime and daytime sleep were assessed on four separate occasions by polysomnography (red hashed bars). Subjective and objective measures of alertness and saliva samples for melatonin assays were collected every 2 h on the first and fourth night shifts under baseline and intervention conditions (red filled circles). Transmission profile (B) of the filtered light (blue line) was generated against a standard fluorescent light source (black dashed line), demonstrating the effective visual short-wavelength range (<480 nm; gray-shaded region) removed by the interference filters.