It is known that every human activity is better carried out in the presence of natural light than in the absence of it. This is probably due to the comfortable feeling of the occupants respect to the perception of the flowing of time, which is impossible when artificial lamps are the only light sources in the environment. In many cases the natural light is absent, as in underground areas of a building, or insufficient, as in the case of large plant area rooms, where the windows on the perimeter walls are not able to illuminate the whole environment being too small or too distant from the centre of the room. Moreover the indiscriminate use of electric light even if the daylight is available, due to a deplorable habit of the occupants of the workplaces, is a fairly common practice and it increases the energy consumption in buildings that already covers about 40% of the total energy consumed worldwide.