Improving Illumination in Inspection Operations for Products with a Significant Specular Reflection Component

V. D. Nikitin, R. I. Zakirov

(Presented by the scientific seminars of the Departments of Lighting Engineering and Light Sources and of Electrical Systems and Networks)

The distribution of brightness in the field of view is one of the most important indicators of the quality of illumination. A system of general lighting alone has certain hygienic and psychological advantages precisely because of the more favorable distribution of brightness in the field of view. However, abandoning a combined-lighting system and switching to general lighting alone is associated (within the framework of the current standards, which establish separate normalization of the magnitude of illumination for the two systems) with the need to reduce the illumination of the workplace by approximately a factor of three. Although the qualitative and quantitative indicators of lighting are interrelated, they do not replace one another, and not every reduction in illumination can be compensated for by creating a favorable distribution of brightness in the field of view [1].

At the same time, the relatively higher illumination in a combined-lighting system is associated with an a priori nonuniformity of the brightness distribution in the field of view. Here the question of the permissible limits of this nonuniformity becomes central; in other words, the question of the ratio between the illumination from general and local lighting in a combined system.

The current standards for artificial lighting require that the illumination from the general-lighting system on working surfaces and in the zones adjacent to them be not less than 10% of the total illumination in the combined-lighting system. The creation of illuminations greater than 200 lx (with incandescent lamps—100 lx) is not required. Thus, the standardized share of general lighting proves to be a function of the standardized illumination, i.e., it depends on the nature and conditions of the work. However, analysis of this dependence for precision (I, II, III

Fig. 1. Relative weight of general lighting in a combined-lighting system

... category) of visual tasks revealed that, as the intensity of the visual task increases, the relative share of general lighting does not increase but, on the contrary, decreases (Fig. 1). Thus, in precision visual tasks, a favorable distribution of brightness in the workers’ field of view may not be ensured.

The advantages of a system of general lighting alone (favorable distribution of brightness in the field of view) and of combined lighting (comparatively high illuminance) are united in the system of “combined lighting with intensified general lighting” [2]. It represents a compromise between the desire to create illuminance of the working surface (and the zone adjoining it) only from general lighting, in view of the optimum of visual functions under a uniform distribution of brightness, and the necessity, caused by the specifics of the visual task and/or economic considerations, of having local lighting.

The share of general lighting in the system of “combined lighting with intensified general lighting” should be chosen so as to cover the interval of the most significant increase in visual functions when increasing the relative share of general lighting in the combined system. Let us consider, as an example, the operation “inspection of bases” of category IIIb+1, for which, under the current standards, with gas-discharge lamps, illuminance \(E_1 = 300\) lx and \(E_2 = 1000\) lx is required, respectively, in the system of general lighting alone and combined lighting (in the latter case, the share of general lighting accounts for 100 lx). In the proposed system of “combined lighting with intensified general lighting,” the illuminance from general lighting \(E'_{\mathrm{gen}}\) and the total illuminance \(E'_{\mathrm{comb}}\) are expressed by the formulas:

\[ E'_{\mathrm{gen}} = 0.5 E_{\mathrm{gen},1} + 0.5 E_{\mathrm{gen},2} \quad \text{and} \quad E'_{\mathrm{comb}} = E'_{\mathrm{gen}} + 0.5 E_{\mathrm{loc},2}. \]

Fig. 2. Ratio of illuminance for three lighting systems

Fig. 3. Nomogram for calculating combined lighting with intensified general lighting

A visual ratio of the illuminance from three lighting systems is presented in Fig. 2, and a nomogram for the calculation is given in Fig. 3. Verification on experimental lighting installations in the electrolamp industry showed that, in terms of energy consumption, the system of “combined lighting with intensified general lighting” is equivalent to the system of general lighting alone and to ordinary combined lighting, while surpassing them in lighting-engineering and hygienic respects.

We shall show the application of the system of “combined lighting with intensified general lighting” using the example of a base-inspection section, where intensified general lighting is combined with local lighting that performs specific tasks.

The intensified general lighting of the section \((E'_{\mathrm{gen}} = 200\) lx) was provided by luminaires with diffuse light distribution, ShOD-2×40, which

provides a favorable distribution of brightness in the illuminated room. To create the best conditions for seeing plinths (which have a complex relief and, in some cases, a substantial specular component of reflection), local lighting is required in the form of a luminous surface of definite dimensions and orientation [3]. Reflected in the plinth, a luminous surface of uniform and moderate brightness forms on it an artificial light background, against which, owing to the increase in contrast, various defects of the plinths—scratches, dents, marks, torn contacts, spots, etc.—are clearly distinguished.

Solving the problem of eliminating reflected glare and increasing the contrast of defects against the background by means of general-purpose luminaires is difficult or impossible; therefore experimental luminaires A and B, with fluorescent lamps and incandescent lamps, were designed and built for local lighting of this operation [4].

The brightness of the luminous surface of the luminaires is shown in Fig. 4, and the cylindrical illuminance they create is shown in Fig. 5. It is evident that the space beneath the luminaires is fairly saturated with light, which is of special importance in view of the complex relief of the plinth surface and the presence inside it of a cavity with a dark glass compound at the bottom.

Fig. 4. Brightness of the luminous surface of the luminaires (2, 4, 6, 8, 12—number of lamps switched on)

Fig. 5. Cylindrical illuminance from experimental luminaires

The best results were obtained in the case of luminaire A with LB-40 lamps, with a diffuser brightness of 1500 nt and an illuminance (horizontal) at the workplace of 600–800 lx (from local lighting). However, it should be emphasized that the magnitude of the illuminance on the surface of specularly reflecting parts, including plinths, is of less importance for the visibility of defects than the brightness and dimensions of the luminous surface.

As a result of creating, in the plinth inspection area, intensified general lighting in combination with local lighting that solves specific tasks, an increase in labor productivity of 8% and a reduction of defective work by 45% from the previous value (at \(E_{\text{gen}} = 100\) lx) were established with confidence probability \(p = 0.95\). This demonstrates the high effectiveness of the measures for improving lighting.

REFERENCES

1. V. V. Meshkov and Z. B. Smelyanskii. Lighting Hygiene. Moscow, 1934.
2. V. D. Nikitin. A system of combined lighting with intensified general lighting as a factor in increasing labor productivity. In: Acceleration of the Technical Process—a Path to Increasing Production Efficiency. Proceedings of the Intersectoral Scientific-Production Conference. Tomsk, 1970.
3. A. S. Shaikevich. The Quality of Industrial Lighting and Ways to Improve It. Moscow–Leningrad, 1962.
4. V. D. Nikitin. Information Leaflet No. 29 of the Tomsk TsNTI. Tomsk, 1969.