Daylight, rather a fact than a matter of discussion for many millennia, has lost its dominant role in architecture during the years 1950 till 1965. The artificial lighting of interiors had reached its long promised goal and was considered superior to daylighting in quality. In many countries, office buildings and even schools were built without windows because the new techniques of lighting and air conditioning were believed to perform much better than conventional lighting from windows and skylights and air supply through wall openings. Studies of the ERGONOMIC Institute, Berlin, in German office buildings, published first in 1990, revealed that almost 60 % of the workers considered lighting a health hazard, and, in addition, that in work spaces where artificial lighting dominates the self-reported state of health of workers was far below of those working in areas with daylight dominance.Since this was not only true for „vision-related“ symptoms like eye fatigue, but also with other health complaints related to temperatures or noise we assumed that the effects are likely to be caused by influences of lighting on the hormonal system. During the 1990s, a series of studies on the impact of lighting on humans were performed in the USA. They included offices, schools and retail buildings. The outcome in short is, that daylight was demonstrated to improve human performance, to change the state of health for the better, to help boosting sales in retail shops. In addition, other studies have demonstrated its impact on the energy efficiency of buildings.