In the course of evolution, the biological rhythm of all living beings has adapted to the natural course of day and night, with the internal clock and therefore sleep-wake cycles being controlled significantly by daylight. If people mainly spend their time outdoors, the changes in natural daylight will give them the exact light their bodies need: bright, cold white light with a high blue component in the morning and during the day, and less bright, warm white yellow-reddish light without blue components in the evening.
The problem is that in our modern industrial and service-based society most people spend about 90 percent of their day in enclosed spaces under artificial light. This already applies to young people who throughout their entire education – from school and vocational training to university – spend a lot of time during the day in mostly poorly lit teaching and seminar rooms or auditoriums.
How much the changes in light between day and night influence what is known as the circadian rhythm, which is actually fully geared toward outdoor life, people notice not only after a long-haul flight but quite clearly twice a year – when the clocks change between summer and standard time and many feel uncomfortable, experiencing effects similar to a mini jet lag. A survey in the European Union on whether the time change should be scrapped therefore created a clear majority in 2018 for a uniform time throughout the year.