The importance of light as 'Zeitgeber' for the internal biological clock receives an increasingly higher priority. There is evidence to assume that under daily life situations lighting conditions are often not sufficient to synchronize the internal clock to the external 24-h-rhythm. In addition, the lighting during the day can significantly contribute to our alertness and performance. In our study we wanted to test the extent to which blue-enriched light exposure in the morning can acutely improve subjective alertness and performance, and whether it can stabilize the circadian phase and improve sleep over several days. An additional goal was to evaluate and analyze different light situations with regard to potential risks (e. g. negative influences on alertness, performance, sleep, circadian clock, etc.). The study was conducted with 18 healthy young subjects in a cross-over within-subject design and lasted for 8 days. The volunteers spent the evenings, nights and mornings in the laboratory and were exposed for 30 minutes in the evening to three different lighting conditions (in a randomized order). The following morning, they were then exposed for three hours either to an office lighting with polychromatic blue-enriched light, or to control light with a polychromatic warm white light bulb at much lower illuminance. The results showed that the lighting in the morning had an acutely wake-promoting effect, and participants showed faster response times in a sustained vigilance task. In the evening, the morning light still had an impact on their performance, and subjective sleepiness increased less rapidly when they had received the blue-enriched light in the morning.
With all variables, we also found positive effects over several days with the blue-enriched morning light. During nighttime participants spent less time in stage 2 sleep when they were in the warm-white lighting condition, whereas total sleep time, deep sleep and REM sleep were similar after both morning light conditions. The quantification of the sleep EEG activity revealed higher power in some frequency ranges (> 7 Hz) during NREM sleep after the morning warm white light bulb condition. A core topic of this study was the circadian phase shift, which can be induced by light at the wrong time. Under the blue-enriched lighting in the morning we found that the circadian phase of salivary melatonin was overall less shifted, in comparison with the warm white light in the morning. Our results give further evidence that a suitable morning light has a balancing, stabilizing effect on the circadian system, and so to speak, is a counter-strategy for insufficient lighting or light at the wrong time.
Please download the complete report "Circadian effects of AmI-based lighting systems: Effects of circadian desynchronization" (in German only).
Circadiane Wirksamkeit AmI-basierter Beleuchtungssysteme: Wirkungsfragen circadianer Desynchronisation.
1. edition. Dortmund: Bundesanstalt für Arbeitsschutz und Arbeitsmedizin 2015.
ISBN: 978-3-88261-148-9, pages 20, Project number: F 2302, PDF file