Measuring circadian light and its impact on adolescents.

A field study was conducted with eighth-grade students to determine the impact of morning light on circadian timing, sleep duration and performance. Before and during school hours for a week in February 2009, half the students studied wore orange glasses that minimized short-wavelength light exposure needed for circadian system stimulation. A control group did not wear the orange glasses. The Daysimeter, a circadian light meter, measured light/dark exposures in both groups for seven days. Circadian timing was significantly delayed for those students who wore orange glasses compared to the control group. Sleep durations were slightly, but not significantly, curtailed in the orange-glasses group. Performance scores on a brief, standardized psychomotor vigilance test and self-reports of well-being were not significantly different between the two groups.