The Effect of Spectral Quality of Light on Visual Performance and Fatigue*

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Abstract
There is a large but inconclusive amount of literature on the effects of the color of light on single visual functions, such as visual acuity. The amount of dependable information on the effects of the spectral quality of illumination on work performance is negligible. It was the purpose of the present study to investigate this problem. The work test involved recognition of very fine details (letters) and was designed to reproduce the essential features of conveyor inspection. The standard duration of work was 2 hours. Output, results of a large array of tests of visual functions, subjective reactions (complaints), and subjective preferences were considered as criteria in judging the relative superiority or inferiority of the three illuminants compared (ordinary inside frosted lamps; “natural white” lamps with a white, slightly bluish coating; and Verd-A-Ray lamps having a greenish coating). The illumination intensity (5 ft.-c, 100 ft.-c, and 300 ft.-c) on the work place was made identical for all three lamps. Statistically significant differences between the illuminants were established with reference to a number of criteria of performance and fatigue. The differences were, in general, in favor of the illuminant with greenish coating. The present study used commercially available illuminants. Further systematic studies designed to determine the optimal spectral characteristics of light are needed.

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