The main indicator of natural light in rooms is KEO – the coefficient of natural light . KEO is the percentage ratio of illumination on a given horizontal surface indoors (level 0.8 meters from the floor or floor level) – E pom to one-time illumination by diffused light in the open air – E bunk :
KEO = (E pom • 100%) / Enar
Distinguish between the normalized (KEO p – calculated) and the actual (KEO f ) values. The normalization of KEO settlement is carried out at the design stage of buildings according to a special formula,
taking into account the coefficients of light climate and sunshine, the shading coefficients of windows of opposite buildings, the transmittance, reflection and others, depending on the location of the buildings and their functional purpose . The minimum value of KEO p is taken for points located at a distance of 1 meter from the inner wall at the level of the conditionally working surface – 0.8 meters from the floor.
KEO f is determined by the photometric method, based on the simultaneous measurement of the level of natural light at the studied point and under the open sky using a light meter (the operating principle and determination procedure are given below, in the section “Artificial lighting”).
For classrooms, laboratories, dressing rooms and procedures with side lighting, KEO should be at least 1.5–2% (exact work); for residential premises, hostels, etc. – 0.5-1% (work of medium and low accuracy); for auxiliary premises – 0.3% (rough work); for corridors, walkways, stairs, warehouses – 0.1-0.2%.