We have by late October entered wintertime, or normal time that is the more correct term. The question of use of daylight savings time have caused debate were the public, politicians and research have had at times different viewpoints.
An important task for us engaged in biological rhythms and light research is to give reasons for maintaining normal time rather than daylight savings time all year around. Most people have found that light immediately gives us more energy and makes us alert. These positive effects are connected to the ability of bright light to activate the arousal system of the brain.
To obtain a ”light pulse” in the afternoon may contribute to active free time activities after work, also outdoors. This is a benefit of summer time with brighter evenings in spring and summer.
The light researcher also tries to predict what will happen to us during the rest of the year. From this perspective we have to keep in mind, light influences the regulation of 24-hour rhythms apart from affecting our arousal system. The 24-hour, or circadian, regulation forms part of a slow acting influence of brain processes were light exposure one day is affecting the circadian rhythm the next day.
The circadian regulation is fundamental and important for us to be able to maintain focus at work in daytime and to obtain recovery at night. In circadian disruption we get weary, may experience sleep problems and produce worse performance. Normally the daylight influence in spring and summer at Nordic latitudes ensures our circadian system to work properly.
About 80 % of all yearly energy from the sun reaches us during the period March-August. During the period September-February we only obtain 20 %. This results in increased fatigue. Especially groups that do not spend much time in daylight (< 2 hours) report problems. Risk groups are young age groups, especially women and elderly.
Lack of daylight influences circadian regulation and 24-hour rhythms are delayed. Bedtimes are delayed and sleep is shortened. Work and school demand use of alarm clocks. Sleep deficit, circadian disruption and worsened mood are common. Medication has markedly increased among groups with low exposure of daylight.