Does the biological effect of light have a positive influence on the well-being and performance of truck drivers? A research team from Daimler has been exploring this interesting question in the darkness of Finland’s polar night. A total of eight Daimler test drivers simulated two typical working weeks for truckers at the site in Rovaniemi. The truckers alternated between driving for one week in a truck cab with conventional lighting and for another week in a cab with a Daylight+ module that provides additional daylight while driving and during breaks. In order to ascertain the possible benefits of applying daylight inside the truck cab, project manager and head of the experiment Siegfried Rothe from the Daimler research department defined the following statement as a working hypothesis: that an application of biologically effective light with a wavelength of between 460 and 490 nanometres has positive effects. He designed a sophisticated series of experiments in order to obtain valid results.

Light gives structure to life
Light is one of those things that most people don’t give a great deal of thought to – provided that they aren’t suffering from a lack of light themselves. And yet light dictates how life on Earth is organised. Among other factors, the shift from day to night and back again provides structure as a short-term time cycle, as do the changing seasons. Evolution means that a number of internal clocks have adapted to these circumstances and these help to synchronise our circadian rhythms. What is particularly important in this context is regular switching between day and night. For many years, scientists have been researching the complex relationships between the availability of biologically effective light and the physical and mental states of human beings. Various related health problems have been defined. One of the most common is seasonal affective disorder (SAD). A lack of light is a serious problem for many people in the countries of Northern Europe, for example, where it barely gets light during the winter months and this can result in poor mood, reduced performance and a lack of motivation. Light therapy is a standard method of treating these symptoms medically and of successfully combating them.

Drivers were compared only against themselves
The idea for Daylight+ arose during the course of a series of experiments at the sleep lab at the University of Regensburg. Daimler researcher Siegfried Rothe is involved in numerous projects to help improve working and living conditions for truck drivers and therefore to improve the image of this occupation. He subsequently determined that, due primarily to the outline shape of a conventional truck cab, only a comparatively low percentage of natural daylight reaches the driver’s light receptors. This finding prompted Rothe to think about potential solutions. The results of an initial series of experiments with engineers from the test drive department were unambiguous. The subjective condition of all test subjects improved significantly under the influence of an additional dose of light, regardless of the time of day. Another finding proved surprising: the test drivers with more daylight in the cab drove more economically.

During the experiments in Rovaniemi, the test subjects were only ever compared against themselves. That is, the experiments examined how a driver’s performance changes when they are exposed to additional biologically effective daylight under clearly defined conditions. The extra dose took three forms involving different intensities:

  • Steady light while driving, whereby the intensity was adjusted to the exterior light level.
  • An intense light shower of maximum intensity during the tests before and after driving.
  • Light while reclined, likewise of maximum intensity, during breaks while the driver relaxes in their seat, which has been positioned for a power nap.

During the night, the test subjects slept in a normally darkened truck. For the test drivers, these experiments in the Arctic Circle were a tough test of their capabilities. The team documented the test results with support from co-researcher Dr Michael Schrauf and the use of electroencephalography (EEG), electrocardiography (ECG) and electrooculography (EOG) and other physiological measurements, as well as saliva samples (to ascertain levels of the sleep hormone melatonin). Mental state and professional performance, which are closely related, were examined using standardised psychological test procedures (sustained attention and reaction tests on the computer) and by recording vehicle data through the FleetBoard telematics system.

At the end of the two-week cycles, the individual drivers were interviewed, having previously recorded their subjective impressions. Richard Schneider and Philippe Strasser, two truck test drivers for Daimler, spent time in the Arctic Circle at the darkest time of the year, just before the winter solstice. Both of them expressed enthusiasm for Daylight+ separately. Feedback from the truck test drivers also provided a new insight for Siegfried Rothe. The drivers consistently reported that they perceived the space inside the cab to be considerably more pleasant with the additional light fitting.

„When designing the series of tests, we hadn’t even considered that the space might appear larger,“ admitted the head of the experiment. Rothe estimates that it will take several months to sift and analyse the extensive data from the series of experiments conducted in the Arctic Circle. „Only then we will be able to make a recommendation as to whether the test findings should advisably lead to changes in the design of cab lighting.“

Source: Daimler Trucks