Journal
SCANDINAVIAN JOURNAL OF WORK ENVIRONMENT & HEALTH
Volume 37, Issue 5, Pages 437-445Publisher
SCANDINAVIAN JOURNAL WORK ENVIRONMENT & HEALTH
DOI: 10.5271/sjweh.3144
Keywords
circadian clock; chronotype; field study; light environment; light power spectrum; office worker; sleep-wake cycle
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Funding
- Daimler-Benz-Foundation
- EU
- Siemens AG
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Objectives Circadian regulation of human physiology and behavior (eg, body temperature or sleep-timing), depends on the zeitgeber light that synchronizes them to the 24-hour day. This study investigated the effect of changing light temperature at the workplace from 4000 Kelvin (K) to 8000 K on sleep-wake and activity-rest behavior. Methods An experimental group (N=27) that experienced the light change was compared with a non-intervention group (N=27) that remained in the 4000 K environment throughout the 5-week study period (14 January to 17 February). Sleep logs and actimetry continuously assessed sleep-wake behavior and activity patterns. Results Over the study period, the timing of sleep and activity on free days steadily advanced parallel to the seasonal progression of sunrise in the non-intervention group. In contrast, the temporal pattern of sleep and activity in the experimental group remained associated with the constant onset of work. Conclusion The results suggest that artificial blue-enriched light competes with natural light as a zeitgeber. While subjects working under the warmer light (4000 K) appear to entrain (or synchronize) to natural dawn, the subjects who were exposed to blue-enriched (8000 K) light appear to entrain to office hours. The results confirm that light is the dominant zeitgeber for the human clock and that its efficacy depends on spectral composition. The results also indicate that blue-enriched artificial light is a potent zeitgeber that has to be used with diligence.
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