NIOSH 1975 Mar:52-61
The effect of reducing the levels of illumination on visual performance was discussed. Tests have demonstrated that at low luminance levels, a change as small as one log unit alters the sensitivity of the eye by an equal amount. The drop in the corresponding curve was shown to be accompanied by an increase in the sensitivity of the eye. The ability of the eye to detect differences in luminance was affected by changes in the level of light. Cutting down the lighting level by a factor of two to one changed the ability of the eye to detect differences in luminance, which is the basic feature of visual function. Natural variations in the size of the pupil were used to determine the effect of lighting on visual performance. Tests revealed that the pupils of older individuals did not present the same changes as the pupils of younger individuals. The probabilistic nature of vision was reviewed with emphasis on visual thresholds and suprathresholds. It emerged that the use of thresholds was inadequate because it prescribed levels of light at which half the individuals tested could not see anything half the time. On the contrary, in the tests carried out using visibility suprathresholds, the test subject could see in 99.99 percent of the cases. A visibility suprathreshold corresponding to eight times the threshold, the basis of an international lighting standard, was based on the fact that contrast had to be reduced by one eighth before an individual could see half the time.
Lighting-systems; Eye-disorders; Visual-perception; Health-hazards; Safety-measures; Occupational-health; Eyesight; Visual-motor-performance;
DHEW (NIOSH) Publication No. 75-142
The Occupational Safety and Health Effects Associated with Reduced Levels of Illumination. Proceedings of a Symposium, July 11-12, 1974, Cincinnati, Ohio, NIOSH, Division of Laboratory and Criteria Development, HEW Publication No. (NIOSH) 75-142