Abstract
Improving indoor lighting conditions at the workplace has the potential to support proper circadian entrainment of hormonal rhythms, sleep, and well-being. We tested the effects of optimized dynamic daylight and electric lighting on circadian phase of melatonin, cortisol and skin temperatures in office workers. We equipped one office room with an automated controller for blinds and electric lighting, optimized for dynamic lighting (= Test room), and a second room without any automated control (= Reference room). Young healthy participants (n = 34) spent five consecutive workdays in each room, where individual light exposure data, skin temperatures and saliva samples for melatonin and cortisol assessments were collected. Vertical illuminance in the Test room was 1177 ± 562 photopic lux (mean ± SD) , which was 320 lux higher than in the Reference room (p < 0.01). Melanopic equivalent daylight (D65) illuminance was 931 ± 484 melanopic lux in the Test room and 730 ± 390 melanopic lux in the Reference room (p < 0.01). Individual light exposures resulted in a 50 min earlier time of half-maximum accumulated illuminance in the Test than the Reference room (p < 0.05). The melatonin secretion onset and peripheral heat loss in the evening occurred significantly earlier with respect to habitual sleeptime in the Test compared to the Reference room (p < 0.05). Our findings suggest that optimized dynamic workplace lighting has the potential to promote earlier melatonin onset and peripheral heat loss prior bedtime, which may be beneficial for persons with a delayed circadian timing system.
Highlights
Improving indoor lighting conditions at the workplace has the potential to support proper circadian entrainment of hormonal rhythms, sleep, and well-being
We explored the effects of an automated dynamic lighting control on three circadian markers, melatonin, cortisol, and distal–proximal skin temperature gradient (DPG), by optimizing mixed daylight and electric lighting during office hours
The timing of melatonin onset and peripheral heat loss (DPG) relative to habitual sleep times occurred significantly earlier in the Test than in the Reference room. These results suggest that the use of an automated controller together with an optimized lighting system during the day has the potential to advance circadian phase markers, even under semi-naturalistic conditions in the presence of electric light in the evening
Summary
Improving indoor lighting conditions at the workplace has the potential to support proper circadian entrainment of hormonal rhythms, sleep, and well-being. We tested the effects of optimized dynamic daylight and electric lighting on circadian phase of melatonin, cortisol and skin temperatures in office workers. Wright and colleagues conducted several studies with only daylight exposure and lighting from fireplaces while camping They compared the results of melatonin secretion patterns and sleep timing of the same study participants when they were living and working in their habitual indoor environments, with less light during the day and additional electric light in the evening[22]. The authors found that exposure to natural light during the day led to a circadian phase-advance of the onset of melatonin secretion in the evening of about 2 h (compared to habitual mixed electric and daylighting conditions), which was more pronounced in later than earlier chronotypes. Regarding the impact of light exposure on the circadian modulation of cortisol concentrations, bright light in the early morning increased the morning p eak[43,44], advanced the circadian phase of c ortisol[34,45] and acutely suppressed cortisol concentrations (after 6.7 h bright light exposure, starting around the melatonin peak at night)[46]
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