Document Detail

Daily and seasonal variation in the spectral composition of light exposure in humans.
MedLine Citation:
PMID:  19637047     Owner:  NLM     Status:  MEDLINE    
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.
Helen C Thorne; Kay H Jones; Stuart P Peters; Simon N Archer; Derk-Jan Dijk
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Chronobiology international     Volume:  26     ISSN:  1525-6073     ISO Abbreviation:  Chronobiol. Int.     Publication Date:  2009 Jul 
Date Detail:
Created Date:  2009-07-28     Completed Date:  2009-10-08     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8501362     Medline TA:  Chronobiol Int     Country:  England    
Other Details:
Languages:  eng     Pagination:  854-66     Citation Subset:  IM    
Surrey Sleep Research Centre, Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey, UK.
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MeSH Terms
Circadian Rhythm
Genetic Variation
Photochemistry / methods
Research Design
Rod Opsins / chemistry,  genetics
Grant Support
//Biotechnology and Biological Sciences Research Council; //Wellcome Trust
Reg. No./Substance:
0/Rod Opsins; 0/melanopsin

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