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Daily and Seasonal Variation in the Spectral Composition of Light Exposure in Humans

Thorne, HC, Jones, KH, Peters, SP, Archer, SN and Dijk, DJ (2009) Daily and Seasonal Variation in the Spectral Composition of Light Exposure in Humans CHRONOBIOL INT, 26 (5). 854 - 866. ISSN 0742-0528

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Abstract

Light is considered the most potent synchronizer of the human circadian system and exerts many other non-image-forming effects, including those that affect brain function. These effects are mediated in part by intrinsically photosensitive retinal ganglion cells that express the photopigment melanopsin. The spectral sensitivity of melanopsin is greatest for blue light at approximately 480 nm. At present, there is little information on how the spectral composition of light to which people are exposed varies over the 24 h period and across seasons. Twenty-two subjects, aged 22±4 yrs (mean±SD) participated during the winter months (November–February), and 12 subjects aged 25±3 yrs participated during the summer months (April–August). Subjects wore Actiwatch-RGB monitors, as well as Actiwatch-L monitors, for seven consecutive days while living in England. These monitors measured activity and light exposure in the red, green, and blue spectral regions, in addition to broad-spectrum white light, with a 2 min resolution. Light exposure during the day was analyzed for the interval between 09:00 and 21:00 h. The time course of white-light exposure differed significantly between seasons (p = 0.0022), with light exposure increasing in the morning hours and declining in the afternoon hours, and with a more prominent decline in the winter. Overall light exposure was significantly higher in summer than winter (p = 0.0002). Seasonal differences in the relative contribution of blue-light exposure to overall light exposure were also observed (p = 0.0006), in particular during the evening hours. During the summer evenings (17:00–21:00 h), the relative contribution of blue light was significantly higher (p < 0.0001) (40.2±1.1%) than during winter evenings (26.6±0.9%). The present data show that in addition to overall light exposure, the spectral composition of light exposure varies over the day and with season.

Item Type: Article
Additional Information: This is an electronic version of an article published in Chronobiology International, 26 (5), 854-8. Chronobiology International is available online at: http://informahealthcare.com/doi/abs/10.1080/07420520903044315
Uncontrolled Keywords: Melanopsin, Blue light, Circadian, Photoreception, Sleep, HUMAN CIRCADIAN PACEMAKER, SHORT-WAVELENGTH LIGHT, BRIGHT LIGHT, AFFECTIVE-DISORDER, MELATONIN SECRETION, ANTARCTIC WINTER, BRAIN RESPONSES, GANGLION-CELLS, SLEEP QUALITY, DIM LIGHT
Divisions: Faculty of Health and Medical Sciences > Biochemistry and Physiology
Depositing User: Symplectic Elements
Date Deposited: 24 May 2012 09:54
Last Modified: 23 Sep 2013 19:18
URI: http://epubs.surrey.ac.uk/id/eprint/289608

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