Sources of natural light are the Sun, diffused light from the sky, and reflected light from the surface of the Earth and the Moon. Natural lighting can be: lateral – through light openings (windows) in the outer walls; the top – through the lights, the light openings in the walls in places where the heights of the building are different; combined – with a combination of top and side lighting.
The disadvantages of natural lighting are its fluctuations depending on the geographical latitude, time of year and day, climatic conditions, cloud cover, which is determined by the concept of the light climate of the area, as well as on the purity of the atmosphere, reflecting the ability of surfaces, the presence of shading objects – buildings, trees, mountains, etc.
The natural lighting of the rooms also depends on their architectural and planning decisions: the number, size and configuration of windows, the thickness of window frames, the type of glazing (single, double, triple); quality and purity of glass; the depth of the room, reflecting the ability of the ceiling, walls, etc.
Of great importance for inhabited premises (wards, operating rooms, living rooms, classes, etc.) is the orientation of the windows on the sides of the horizon, since this mainly depends on insolation – exposure to direct sunlight and insolation room mode – the duration and intensity of their illumination in direct sunlight. In the middle latitudes there are three main types of insolation regime .