Seasonal Variation in Human Illumination Exposure at Two Different Latitudes

Abstract

The authors measured ambient illumination exposure in healthy volunteers in San Diego, California (latitude 32 degrees 43' N, n = 30), and Rochester, Minnesota (latitude 44 degrees 1' N, n = 24), during each of the four quarters of the year, which were centered on the solstices and equinoxes. Subjects wore photosensors on their wrists and lapels (or foreheads while in bed) 24 h per day for an average of 5-6 days per quarter. The maximum of the two illumination readings was stored each minute. Annual average time spent per day in outdoor illumination (> or = 1000 lux) was significantly higher in San Diego than it was in Rochester (p < .04). Daily durations of illumination at or exceeding thresholds of 1, 10, 100, 1000, and 10,000 lux were highly seasonal in the sample as a whole (p < .01 at 1 lux, p < .0001 at other thresholds). Seasonal variation in outdoor illumination was far more pronounced in Rochester than it was in San Diego (interaction p < .001) but remained significant in San Diego (p < or = .03). Seasonal variation in indoor illumination was generally similar in the two cities. The median Rochester subject experienced illumination > or = 1000 lux for 2 h 23 min per day during summer and 23 min per day during winter. The corresponding times in San Diego were 2 h 10 min and 1 h 20 min. Neither age nor gender predicted illumination duration at any level. Both season and geographic location strongly influenced human illumination exposure, and behavior (choice of indoor vs. outdoor environment) was the most important mediating factor.

Office workers’ daily exposure to light and its influence on sleep quality and mood

“…[18][19][20][21] According to the literature, no significant differences in daily exposure to light have been found for differences in age, sex, 15,16 income level and family status 15 nor for light on workdays compared to days off. 15,19 Significant differences in the daily exposure to light have been found for differences in geographic latitude and season 16,[22][23][24] as well as occupation. 17,25 Findings are inconclusive for SAD scores: while Espiritu et al 15 found that healthy persons with higher SAD scores spent less time at higher illuminances compared to healthy ones with lower SAD scores Guillemette et al 22 could not find differences between these groups.…”

“…9 Before new devices [10][11][12] for measuring the blue spectral component irradiance were available, data could only be collected for illuminance. Some measurements were taken with devices fixed on the wrist, [13][14][15][16][17] but other, more relevant ones, were taken with devices fixed on the forehead. [18][19][20][21] According to the literature, no significant differences in daily exposure to light have been found for differences in age, sex, 15,16 income level and family status 15 nor for light on workdays compared to days off.…”

“…Some measurements were taken with devices fixed on the wrist, [13][14][15][16][17] but other, more relevant ones, were taken with devices fixed on the forehead. [18][19][20][21] According to the literature, no significant differences in daily exposure to light have been found for differences in age, sex, 15,16 income level and family status 15 nor for light on workdays compared to days off. 15,19 Significant differences in the daily exposure to light have been found for differences in geographic latitude and season 16,[22][23][24] as well as occupation.…”

Seasonal variation in nativity and mortality and in socioeconomic conditions in a single family residing at different latitudes: Germany versus South Africa

“…It is well known that photoperiod greatly varies with latitude. Even a small difference in latitude (San Diego, CA, USA [32° 43′ N], versus Rochester, NY, USA [44° 1′ N]) results in a significantly greater seasonal variation in outdoor illumination in Rochester than in San Diego 20 during each of the four quarters of the year. To the best of my knowledge, it has not yet been studied whether residing at different latitudes results in different seasonal rates in natality and mortality in a single family with more or less the same genetic background.…”

The Influence of Light Exposure and Seasonal Changes on Short-Term and Longer-Term Changes in Axial Length of the Human Eye

“…In a previous study, quantifying light exposure in adults (aged from 21 to 76 years) in the United States over a 6 day measurement period, Cole et al (1995) reported that light measures (time exposed to >1000 lux) derived from 2 measurement days accounted for 75% of the variance of measures derived from their full 6 days of data. This contrasts with our current findings where using 2 days of data explained less than 40% of the variance of our 14-day data in adults.…”