Study confirms influence of artificial light on shift workers
Shift work throws the internal clock out of sync and means stress for the body. One of the reasons for this is that long phases of artificial light exposure disturb the natural day-night rhythm. Fraunhofer UMSICHT used an experimental lighting system at the BMW Group plant in Munich to investigate the influence this has on the body and mind.
Around 6 million people in Germany work shifts – and the trend is rising. This stresses the body. The consequences are diverse and range from sleep problems to heart, circulation and gastrointestinal disorders. Social life and psychological well-being usually suffer. “If we turn night into day, our internal clock gets out of sync because our natural sleep-wake rhythm is oriented to the path of the sun,” say ILIGHTS overall project manager Rasit Özgüc, Department of Photonics and the Environment at Fraunhofer UMSICHT, and project partner Dr. Alfred Wiater, sleep physician at Porz am Rhein Hospital.
Photoreceptor also reacts to artificial light
But it is not only the sun that has an influence on us. Research shows that artificial light – as it occurs in shift work, for example – also has a non-visual effect on the body. In 2002, researchers discovered a third photoreceptor in addition to the rods and cones already known: the intrinsically photosensitive retinal ganglion cells. Their highest sensitivity lies in the blue area of the light spectrum. But to what extent and in what form does artificial light affect the body and mind? Which lighting parameters are ideal for which application? What kind of light increases employee satisfaction? Research is still in its infancy when it comes to answering these questions: There is a lack of data and experimental methods to investigate the complex interactions between employees, work tasks and lighting situations under real conditions.
Targeted selection of lighting scenarios
This is where the ILIGHTS project comes in. In a study period of 6 months and a total project period of 30 months, researchers from Fraunhofer UMSICHT and sleep researchers from Porz am Rhein Hospital investigated the non-visual benefits of LED technology with the aim of improving the lighting situation for employees working alternating shifts. The parameters studied included sleep behavior, cognitive performance, and daytime sleepiness. A production section at the BMW Group plant in Munich was equipped with a specially developed lighting system. The innovative LED experimental system developed by Fraunhofer UMSICHT makes it possible, among other things, to control the lighting dynamically. “In addition to light intensity, individual wavelength ranges in the full spectrum can be regulated precisely,” explains Özgüc.
Sleep researchers at Porz am Rhein Hospital examined the sleep-associated parameters of shift workers in the plant. They took into account the effects of five light phases with different settings of color temperature, melanopic and visual illuminance (melanopic illuminance = spectral illuminance assessed with a biological spectrum of activity, Smel, with maximum sensitivity in the blue range, at a wavelength of λP=480 nm). A total of 83 BMW employees were equipped with a fitness tracker to record their sleep-wake behavior.
The evaluation of satisfaction with the previous lighting situation (baseline) simulated with the experimental system showed that this was lowest among the participants with warm white and dynamic light. The general feeling of well-being was most positive under cold white light with high visual and melanopic illuminance. In the concentration test and daytime sleepiness measurement using pupillographs, the participants showed better results in the light phases with dynamic and neutral white light than in the initial situation before light installation and with warm white light. “However, the positive effect in the concentration test may also only be a training effect,” notes Prof. Andrea Rodenbeck, biologist and sleep researcher. Further tests are required here. A clinically significant improvement in daytime sleepiness and a subjective improvement in general condition were found when looking at the subgroup of participants with an elevated score on the Epworth Sleepiness Scale – a questionnaire to assess daytime sleepiness. In a targeted examination of some participants with a lower overall sleep in baseline, sleep lengthened significantly.
Positive effects on the sleep-wake rhythm
As expected by the researchers, the statistical analysis of the data on sleep-wake behavior collected by the fitness trackers showed no significant changes in the parameters in the early shift. In the late shift, however, there was a trend for cold white to neutral white light to have a positive effect on the rhythm.
“The individual light phases lasted an average of four weeks. Now we have to investigate how the effects behave in long-term studies,” says Monika Owczarek, psychologist and member of Özgüc’s team. Moreover, the individual consumption of light outside the workplace must also be taken into account in the future by means of a “light history”.
Overall lighting concept for the production areas
Özgüc gives an outlook: “At the final presentation of the project, everyone agreed. Both Elisabeth Wolf, Department of Innovations, Digitalization, Network Management at the BMW Group, who took over the sub-project management for the BMW Group, and Gabriele Klyszcz, Senior Security Engineer at the BMW Group, suggested more in-depth studies.” This also makes sense because the results are significant, but have a high standard deviation. Özgüc continues: “Biodynamic light with inclusion of light components from the light phases with neutral and cold white light at moderate to high melanopic and visual illuminance could have potential. Together with the BMW Group project team, we suggested that the results should be converted into an overall lighting concept for the production areas and implemented; ideally with a subsequent evaluation with a larger sample size and a longer period than ILIGHTS.”
UMSICHT: zur Sache!
You can read more about the results on April 11, 2019, as part of the “Umsicht: zur Sache!” workshop at Fraunhofer UMSICHT in Oberhausen. The topic: “Light and Health”. Further information about the event will soon be available on the Fraunhofer UMSICHT website.
The “ILIGHTS” joint project ran from mid-2016 to the end of 2018 and was financially supported by the German Federal Ministry of Education and Research (BMBF) as part of the “Intelligent Lighting” funding initiative (FKZ: 13N14043)
Publications about the project ILIGHTS
- Effects of different light expositions on wakefulness, mood, and attention in shift workers: an ongoing field study in a morning and evening shift system
WILEY, Journal of Sleep Research, S. 119
- Reliabilität von aktimetrischen Fitness-Tracker-Daten in der Schlafforschung
Somnologie 22 (2018), Supplement 1, S. S2
- Wirkung verschiedener Langzeitlichtbedingungen bei Industriearbeitern in wöchentlicher Wechselschicht
Somnologie 22 (2018), Supplement 1, S. S21–S22
Further publications to come.