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These conditions are determined in state building codes for designing buildings and
structures, regulations on building design of structures of some industries approved in
the prescribed manner. Premises in the basement floors of buildings can also have no
natural lighting.

Natural lighting is divided into the side, top and combined (top and side).
Characterization of natural lighting at the workplace in absolute value is impossible
due to its change with time depending on the time of day, time of year and
cloudiness. Therefore, it is taken to normalize the relative value that is the natural
lighting coefficient (NLC).
NLC is the ratio of the illumination at a point inside the room Ein to
simultaneous illumination outside of the room Eout, which is created by the light of
the open sky, %, i. e.

NLC= Eint/Eext · 100 %.

The following factors affect brightness level in conditions of natural
illumination: light climate, square and direction of light openings, degree of glass
cleanness, wall and ceiling color depth of the room.

9.6 Artificial Illumination

There are the next types of artificial illumination:
- general: even and uneven;
- combined: consist of general and local;
- local: concentrates light flux at workplaces.

Local illumination is forbidden to use since it creates the danger of industrial
injuries or occupational diseases.

General lighting provides uniform illumination over the whole working area
and does not limit the positioning of the work (Figure 9.3 a).

General Localised lighting provides different levels of illumination in
different parts of the same working area. It matches the level of illumination to the
needs of specific tasks (Figure 9.3 b).

Combined lighting is usually a combination of background lighting and a
luminaire close to the actual work area.

It is used when:
(a) a high level of illumination is needed in a small area;
(b) flexible directional lighting is required, for example when doing different
tasks at a workstation;
(c) general lighting is unnecessary or impossible to install because of the layout
of the work area (Figure 9.3 c).

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