Circadian Analysis on Human Population Entrainment: Inferences from the Power Grid

Few, if any studies have focused on the daily rhythmic nature of modern industrialized populations. The present study involved actigraphic analyses of continuously streaming electrical load data from a human subject pool of approximately 43 million primarily residential users in the U.S. Pacific Northwest as a reflection of daily household activity. Rhythm analyses reveal striking seasonal and intra-week differences in human activity patterns, largely devoid of manufacturing and automated load interference. Length of the diurnal activity period (alpha) is longer during the spring than the summer (16.64 h versus 15.98 h, respectively; p p p < 0.01). This indicates a general phase-delaying response to the absence of job-related or other weekday morning arousal cues, substantiating a preference or need to sleep longer on weekends. Finally, a shift in onset time can be seen during the transition to Daylight Saving Time, but not the transition back to Standard Time. The use of grid power load as a means for human actimetry assessment thus offers new insights into the collective diurnal activity patterns of large human populations.