Brightness in Visual Field at Borderline Between Comfort and Discomfort (BDC)
Quality of lighting has been defined as a function of the brightness characteristics of certain unique portions of the visual field. The brightnesses of these areas and the brightness-ratios between them contribute favorably or unfavorably to the seeing conditions. They may influence the visibility of a visual task, or their effects may be more subtle, insidious or deep-seated and result in decreased ease of seeing. Obviously, all the effects may be produced simultaneously. In general, it is an easy matter to provide the footcandle-levels within the restricted area of the visual task for the attainment of definite or generally adequate visibility-levels. However, the proper adjustment of all of the brightnesses in the entire visual field is of great importance to the worker who must perform tasks of critical seeing for prolonged periods in the resulting visual environment. Thus the ultimate goal of lighting practice is to provide brightnesses in the entire visual environment which produce the most satisfactory seeing conditions. This can be accomplished only by proper attention to, and application of, what has been termed brightness engineering.