Latitudinal trends in human primary activities: characterizing the winter day as a synchronizer

TL;DR

This study investigates how winter daylight patterns influence human activity schedules across mid-latitude countries, revealing that natural light cues like sunrise and sunset significantly synchronize work and meal times, especially in regions with shorter winter days.

Contribution

It provides a comprehensive analysis of time use data across 19 countries, highlighting the role of winter light conditions as natural synchronizers for daily human activities, which was less understood before.

Findings

Winter sunrise synchronizes labor start times below 54° latitude.

Winter sunset influences labor end times across studied regions.

Dinner times are closely aligned with winter sunset, within a narrow time window.

Abstract

This work analyzes time use surveys from 19 countries (17 European and 2 American) in the middle latitude range from 38{\deg} to 61{\deg} latitude accounting for 45% of world population in that range. Time marks for primary activities (sleeping, working and eating) are systematically contrasted against light/dark conditions related to latitude. The analysis reveals that winter sunrise is a synchronizer for labor start time below 54{\deg} where they occur within the winter civil twilight region. Winter sunset is a source of synchronization for labor end times. Winter terminator also punctuate meal times in Europe with dinner times occurring 3h after winter sunset time within a strip of 1h, which is 40% narrower than variability of dinner local times. The sleep-wake cycle of laborers in a weekday is shown to be related to winter sunrise whereas standard population's cycle appears to be irrespective of latitude. The significance of the winter terminator depends on two competing factors average daily labor time (some 7h30m) and winter daytime ---the shortest photoperiod---. Winter terminator gains significance when shortest photoperiod roughly matches to daily labor time plus a reasonable lunch break. That is within a latitude range from 38{\deg} to 54{\deg}. The significance of winter terminator as a source of synchronization is also related to contemporary year round time schedules: the shortest photoperiod represents the worst case scenario the society faces. Average daily sleep times show little trend with the shortest photoperiod slope 5min/h for a Pearson coefficient $r^2=0.242$. Average labor time may have a weak coupling with the shortest photoperiod: slope 29min/h for $r^2=0.338$.