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The trigonometric table

3. The aperture angle g determination (CAD angle, under which the part of the sky can be seen from the working place). This angle can be determined as the difference between the angle of incidence a and angle of shading b (DAB angle at the workplace between the horizon and the plane connecting the workplace and the shading object’s top (buildings, trees, mountains) (see the diagram, fig. 4.1).

To determine the angle of shading you must find the point D, where the line (plane) connecting the workplace and the top of the shading object comes through the window, divide the BD cathetus by AB (find the tangent of the shading angle), and find the value of the angle of shading b from the table.

The determination of depth coefficient in different premises - the ratio of the distance from the window to the opposite wall (EF, m) to the upper window edge height above the floor (CE, m). According to the hygienic norms this coefficient must not be higher than 2 for residential areas, classrooms and other similar premises.

The lighting engineering method of natural lighting assessment in different premises consists in determination of daylight factor (DF).

The daylight factor (DF) is defined as the ratio of the actual illuminance at a point in a room (lux) and the illuminance available from an identical unobstructed sky:

The indoor and outdoor lighting is measured by luxmeter (see the instruction, appendix 2 and fig. 4.2).

Fig. 4.2. Luxmeter U-116 (Ю-166)

(1 – measuring device (galvanometer); 2 – light receiver (selenium photo-cell); 3 – changing light filters)

The part of the sky can be hidden behind the tall buildings and trees in the cities or by mountains in highlands. That’s why the curves of the regional lighting climate are used in practice (fig. 4.3).

The curves, shown on the fig.4.3, include months, hours and the level of cloudiness. The ordinate axis has lighting indicators, marked in thousands of lux.

The natural lighting of factory sections may be side (one-side, double-side), upper (light apertures in the ceilings) and combined.

According to the Building Norms and Rules (BNandR)-4-79, the daylight factor (DF) is calculated:

- in case of one-sided lighting – at the distance of 1 m from the opposite wall;

- in case of double-sided lighting - in the middle of the section;

- in case of the combined lighting, the average of the several lighting measurings, performed using the “envelope” method is calculated (table 4).

Fig. 4.3. Curves of light climate

Table 4