Stuttgart - Being in a sunny mood is more than just a saying, and light has a well-documented influence on making us happier, more productive people.

A research team from Daimler, in the darkness of Finland's polar night, has explored how the biological effect of light could have a positive effect on the well-being and performance of truck drivers.

For many people in Northern Europe, where it barely gets light during winter, the aptly-named seasonal affective disorder (SAD) is a serious health problem which results in poor mood, reduced performance and a lack of motivation. Light therapy is a standard method of treating these symptoms, and Daimler's experiment tested whether applying artificial daylight inside cabs improves the mood and performance of truck drivers who tend to spend long periods behind the wheel, often at night.

Head of the experiment, Siegfried Rothe from the Daimler research department, determined that due to the shape of a conventional truck cab, only a comparatively low percentage of natural daylight reaches the driver's light receptors.

So he got eight Daimler test drivers to simulate two typical working weeks for truckers at a site in the Finnish town of Rovaniemi in the Arctic Circle. 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.

The results of the test were as clear as daylight: 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.

The truckers were tested by 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 tests.

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+, and 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 arctic circle experiments. "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."

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.

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.