ON AMENDMENTS TO ARTIFICIAL LIGHTING STANDARDS FOR WORK ON TRANSILLUMINATED BACKGROUND SCREENS AND BY TRANSMITTED LIGHT

V. D. Nikitin

One of the most important characteristics of the conditions of visual work is contrast—luminance or color contrast—between the objects to be distinguished and the background on which they are visible [L1]. It is known that contrast depends both on the properties of the material and, to a large extent, on the lighting conditions.

Contrast affects the resolving power of the eye, which is especially important when distinguishing small details, and is a more effective and economical means of increasing this ability than increasing the illuminance of the working surface [L2]. Contrast also affects such an essential function of vision as the speed of discrimination. Increasing the contrast of the object (objects) of discrimination with the background gives a more noticeable increase in the speed [L3, 4] and success [L5] of discrimination than increasing the luminance of the background.

One of the main tasks of industrial lighting is to increase the contrast of the objects being distinguished with the background. With unchanged values of the reflection coefficients of the background and the object, increasing the illuminance of the working surface does not lead to an increase in contrast. At the same time, the importance of increasing the luminance of the working surface and of the field of view in general as a factor in improving visual functions as a whole must not be underestimated. In addition, increasing the illuminance of the workplace, as a rule, leads to an increase in the visibility of the object of discrimination (although in many cases this task can be solved more effectively by using various lighting-engineering means and lighting techniques aimed at increasing contrast, and without increasing the illuminance of the workplace).

However, in some special cases, increasing the illuminance of the workplace leads even to a negative result, since it reduces the contrast between the object of discrimination and the background. First of all, these include visual operations such as reading images on the screen of a cathode-ray tube or in daytime cinema, certain types of microscopy, reading microfilms on certain devices [L6], reading electroluminescent and radioluminescent devices [L7] and [L8], and analogous operations.

Common to these operations is the projection, onto a transparent background screen, of the image of the object under consideration, which may be “washed out” by light fluxes incident on the surface of the background screen facing the observer.

The luminance \(B_1\) through a screen with transmittance coefficient \(\tau\) is seen by the observer’s eye as luminance \(B_1'=\tau B_1\). The luminance \(B_2\) is reflected from the surface of the screen and is perceived by the observer’s eye as luminance \(B_2'=\rho B_2\). The luminance of the surface at point 0 will be expressed as \(B_1' + B_2' = \tau B_1 + \rho B_2\) (for one and the same surface, and on one side of it, luminances are added arithmetically). It is obvious that, with unfavorable ratios of the fluxes “from the left” and the fluxes “from the right” \((\rho B_2 \geqslant \tau B_1)\), “veiling” of the image on the screen may occur due to luminous fluxes falling from the room onto the outer surface of the screen facing the observer.

Fig. 1

In addition to the examples given above, let us name a number of other operations in electric-lamp production in which increasing the illumination of the workplace may lead to a reduction in the contrast of the object of discrimination with the background and to a loss of visibility of the object:

1) all types of inspection and rejection operations with glass products (flasks, plates, stems, rods, wire, etc.) by transmitted light;

2) focusing the lamp filament in devices that give a magnified shadow image of the filament;

3) counting the number of turns and inspecting the profile of the spiral on a shadowgraph, which also gives a magnified shadow image.

Similar operations are encountered not only in electric-lamp production, but also in other branches of industry; therefore, the question of standardizing lighting for such work has not only academic or merely departmental significance.

The formal assignment of any of the named and related operations to one or another class and subclass of the current artificial-lighting standards, and thereby the determination of the illumination at a given workplace, may lead to a solution that is erroneous from the lighting-engineering point of view. Work of this kind falls outside the “Building Codes and Regulations” (SNiP) and analogous documents, and such work should not be classified and standardized according to SNiP, in order to avoid a negative effect. Rational standardization of the lighting of such work is possible within the framework of sectoral lighting standards.

In view of the fact that SNiP, in our opinion, should not be extended to such work, a proposal is made to introduce an amendment into the existing SNiP, as well as into the “Draft Standards for Artificial Lighting” [L7], which is at the approval stage. The following wording of this amendment is proposed (with reference to the “Draft Standards for Artificial Lighting”).

Clause 13. “The standards for artificial lighting do not apply to work performed on transilluminated background screens and by transmitted light, and the illumination for such work should be standardized not according to Table 1, but according to sectoral standards.”

This clause gives special depth to the words “determined in accordance with the requirements of Table 1” from the current clause 13 of the “Draft Standards ...”

artificial lighting (cited from the journal Svetotekhnika, 1966, No. 1, p. 4):

“Changes in the values of the standardized illuminance determined in accordance with the requirements of Table 1 are permitted, when hygienic or technical-economic substantiations are available, only in industry-specific standards approved according to the established procedure” (for now it is implied that there are also such operations that are not standardized directly by the Building Norms and Rules and that are determined not from Table 1 but directly from the industry-specific standards).

In addition, we propose adding to this last clause the word “lighting-engineering,” since in principle the possibility is not excluded of resolving certain questions of lighting standardization at the level, so to speak, of pure lighting engineering, without recourse to hygienic or technical-economic support.

REFERENCES

1. A. S. Shaikevich. Quality of Industrial Lighting and Ways of Improving It. M.–L., 1962.

2. V. V. Meshkov. Lighting Installations. Moscow, 1947.

3. V. G. Samsonova. Dependence of discrimination time on the angular dimensions of the central field, its brightness, and the ratio of the brightnesses of the peripheral and central fields under conditions of light adaptation. Problems of Physiological Optics, vol. II, 1944.

4. A. S. Shaikevich. Classification of visual tasks. Proceedings of LIOT, Industrial Lighting, 1958.

5. H. C. Weston. The relation between Illumination and Visual Efficiency, Medical Res. Couns., 1945, N 87.

6. I. G. Kovalenko. Physiological-hygienic evaluation of visual work when reading microfilms. Occupational Hygiene and Occupational Diseases, No. 12, 1968.

7. I. P. Slyadnev and others. Radioluminescent light sources with tritium filling. Svetotekhnika, No. 8, 1963.

8. V. P. Derkach and V. M. Korsunsky. Electroluminescent Devices. Kiev, 1968.

9. Draft standards for artificial lighting. Svetotekhnika, No. 11, 1966.