The results of the Algonquin Middle School study demonstrated that it was the extended daylight hours due to the seasonal change, not evening electric lighting after dark in the home, that had the biggest impact on delayed sleeping patterns. According to Figueiro, these results underscore the importance of measuring the 24-hour circadian light and dark patterns in order to draw valid inferences from field studies of this kind.
"This latest study supplements previous work and supports the general hypothesis that the entire 24-hour pattern of light/dark exposure influences synchronization of the body's circadian clock with the solar day and thus influences teenagers' sleep/wake cycles," explains Figueiro. "As a general rule, teenagers should increase morning daylight exposure year round and decrease evening daylight exposure in the spring to help ensure they will get sufficient sleep before going to school."
Measuring "Circadian Light"
In the study, the Algonquin Middle School students were exposed to significantly more "circadian light" in the early evening during spring than in winter, resulting in both delayed melatonin onset and shorter self-reported sleep durations. Each subject wore a Daysimeter, a small, head-mounted device developed by the LRC to measure an individual's exposure to daily "circadian light," as well as rest and activity patterns. The definition of circadian light is based upon the potential for light to suppress melatonin synthesis at night, as opposed to measuring light in terms of how it stimulates the visual system.
This study, sponsored by the U.S. Green Building Council (USGBC) and, in part, by a grant from a Trans-National Insti
|Contact: Mary Cimo|
Rensselaer Polytechnic Institute