ANALYSIS OF THE CAUSES OF UNEVEN BRIGHTNESS DISTRIBUTION IN THE FIELD OF VISION OF WORKERS IN CERTAIN OPERATIONS OF ELECTRIC-LAMP PRODUCTION

V. D. NIKITIN

(Presented by the scientific seminars of the departments of lighting engineering and light sources and of occupational safety)

Brightness is a lighting-engineering quantity to which the visual analyzer responds directly; therefore the distribution of brightness in the field of vision has a most substantial effect on visual performance. It is considered that visual comfort is ensured when

\[ 0.3 \leq \frac{B_{\mathrm{p}}}{B_{\mathrm{c}}} \leq 3, \]

where \(B_{\mathrm{p}}\) and \(B_{\mathrm{c}}\) are, respectively, the brightness of the peripheral and central fields of vision.

Complete uniformity of brightness distribution in the field of vision is not needed—it is precisely differences in brightness that first of all make objects and details distinguishable; moreover, an equal-brightness environment appears unnatural—and it is impossible, for example, because of the different brightness coefficients of objects located in the field of vision [1].

The process of readaptation from one brightness level to another requires almost no expenditure of time when the ratio of the lowest and highest brightnesses does not exceed \(1:10\); therefore a nonuniformity of brightness distribution of \(1:10\) is considered entirely permissible (although the negative effect of the inductive action of differently illuminated areas of the retina is manifested). If there are excessively bright and/or excessively dark surfaces in the field of vision, then the brightness distribution becomes sharply nonuniform, and visual performance decreases because of the inductive action of differently illuminated areas of the retina and the difficulty of readaptation from high brightnesses to very low ones and back.

The limiting ratio between the brightnesses of any two points within the field of vision that is still permissible for hygienic reasons is \(1:40\).

A consequence of uneven brightness distribution in the field of vision is visual fatigue of workers, and in production terms—a decrease in labor productivity and a deterioration in product quality. Nevertheless, sharply uneven brightness distribution is widespread in a number of branches of industry [2], including the electric-lamp industry [3].

In the course of studying lighting conditions at a number of incandescent-lamp manufacturing plants (Tomsk, Leninsk-Kuznetskii, and others),

Table 1

NOTE. Surfaces marked with asterisks do not, under ordinary conditions, fall within the field of view.

the distribution of brightness in the field of vision of persons engaged in certain visually strenuous operations was studied. Brightness was measured by means of a Yu-16 luxmeter and subsequent conversion of illuminance to brightness (for diffusely reflecting or transmitting surfaces), and also with an attachment tube for the luxmeter and a VFM-57 visual photometer. The values given in Table 1 are averages for all workplaces of the same type, with several (3–5) measurements at each place. The mains voltage during the measurements was monitored with a recording voltmeter.

As the table shows, in most cases the ratio \(B_{\mathrm{p}} : B_{\mathrm{c}}\) is far from comfortable. In addition to those mentioned in the table, there were also other surfaces in the field of vision which likewise could act as an additional source of nonuniform brightness distribution.

The study showed that the main causes of nonuniform brightness distribution in the field of vision of workers at electric-lamp plants are:

1) sources of direct glare (light sources and parts of luminaires with increased brightness) due to violations in the installation and operation of lighting installations;

2) an insufficient level of illuminance, especially from general lighting in a combined-lighting system;

3) direct-light luminaires in combination with dark tones of walls and equipment, especially in the presence of shadows.

In addition, unevenness may be caused by errors in creating artificial light backgrounds, reflected glare of luminaires in lamp bulbs, table coverings, etc., the effect of uncurtained window areas in daytime and at night, and so forth.

At the enterprises surveyed, the illuminance of most workplaces that formally had combined lighting was created almost exclusively by local luminaires (Table 2). This

Table 2

also served as one of the main causes of the nonuniform distribution of brightness in the field of vision. At the same time, it should be noted that the illuminance levels required by the standards were almost nowhere fulfilled. If the low level of illuminance can be explained by poor operation of lighting installations (untimely cleaning and replacement, etc.), then the nonuniform distribution of brightness is explained by something fundamentally different—insufficient attention in the current standards for artificial lighting to questions of brightness distribution in the field of vision (SNiP-II V.6-59).

The standards contain no direct regulation of brightness distribution; instead, for the combined-lighting system, where the distribution of brightness is known in advance to be nonuniform, a requirement is put forward that the illuminance from the general-lighting system should constitute at the work—

working surfaces and in the zones adjoining them of at least 10% of the total illuminance in the combined-lighting system, but not less than 100 lx (respectively, with incandescent lamps—not less than 30 lx). The creation of illuminances greater than 200 lx (with incandescent lamps—100 lx) is not required.

In practice this means that what is required is precisely an illuminance equal to 10% of the standard for combined lighting, but not less than 100 and not more than 200 lx (respectively, for incandescent lamps—30 and 100 lx). The only exception is the lighting of skylightless and windowless buildings, where general lighting must provide at least 20% of the standard for combined lighting (for gas-discharge lamps—not less than 150 and not more than 500 lx). Thus, the standardized share of general lighting proves to be a function of the standardized illuminance, i.e., it depends on the nature and conditions of the work.

We consider, in principle, the dependence of the requirements for the distribution of brightness in the field of vision on the precision of the work being performed to be justified. However, an analysis of this dependence (Figs. 1 and 2) for visual tasks of

Fig. 1. Specific weight, %, of general lighting in a combined-lighting system with gas-discharge lamps

grades I, II, and III (corresponding in precision to the most widespread operations in the electric-lamp industry), performed under lighting by fluorescent lamps and incandescent lamps in buildings with natural light and without it, revealed that with increasing precision and intensity of the visual work the specific weight of general lighting does not increase but, on the contrary, decreases. In other words, as the load on the visual apparatus increases, an ever greater nonuniformity of brightness distribution in the field of vision is permitted, i.e., the sign of this dependence is the reverse of what should have been expected. As a result, if for the work in the lower half of the table of illumination standards a favorable or relatively favorable distribution of brightness in the field of vision is ensured, then for more precise work a favorable distribution of brightness is difficult or, in a number of cases, impossible (for example, when direct-light luminaires are used and the reflection coefficients of surfaces in the room are low).

Based on the results of the study, which revealed low quantitative and qualitative indicators of the lighting installations, recommendations were given to the corresponding enterprises to reconstruct the sys-

lighting systems in a number of shops. Thus, at the Tomsk Electric Lamp Plant, the reconstruction of lighting in the main production shops was carried out in 1968–1970 under the direction of the author of this article. In view of the fact that the current standards for artificial lighting (with a combined lighting system) generally do not ensure a favorable distribution of brightness in the field of vision, a system of “combined

Fig. 2. Specific share, %, of general lighting in a combined system with incandescent lamps

lighting with intensified general lighting” [4] was developed. The latter represents a compromise between the desire to create illuminance on the working surface and in the zone adjacent to it solely by means of general lighting, owing to the optimum of visual functions under a uniform distribution of brightness, and the necessity, caused by the specifics of visual work and/or economic considerations, of having local lighting. The share of general lighting in the system of “combined lighting with intensified general lighting” should expediently be taken such as to cover the interval of the most significant increase in visual functions when the specific share of general lighting in the combined system is increased.

Testing on experimental lighting installations in the electric-lamp industry [5, 6] showed that the system of intensified general lighting in combination with local lighting solving specific tasks

— is equivalent, in terms of energy expenditures, to systems of general lighting alone and ordinary combined lighting;

— surpasses them in lighting-engineering and hygienic respects.

LITERATURE

1. N. V. Volotskoi, G. M. Knorring, M. S. Ryabov, and A. S. Shaikevich. Electric Lighting of Industrial and Civil Buildings. Energiya Publishing House, Moscow–Leningrad, 1964.

2. E. L. Kotova. Hygienic significance of brightness distribution in the field of vision of workers. In: Lighting of Industrial Enterprises and Human Working Capacity. Leningrad, 1968.

3. V. D. Nikitin. Experience in reconstructing the lighting system of a shop. Proceedings of TPI, vol. 210 (in press).

4. V. D. Nikitin. A system of combined lighting with intensified general lighting as a factor in increasing labor productivity. Proceedings of an intersectoral scientific-practical conference. Tomsk, 1969.

5. V. D. Nikitin. Information sheets of the Tomsk TsNTI, No. 29, 1969, and No. 37 (67), 1970.

6. V. D. Nikitin. Improvement of lighting in the filament-control section at the Tomsk Electric Lamp Plant. Proceedings of TPI, vol. 223 (in press).