ILLUMINATION CONDITIONS

Our ability to perform tasks that require visual discrimination is greatly influenced by lighting conditions. But in determining the optimum level of light, the character of the object under observation—its size, and the amount of brightness, contrast, and detail it contains—as well as the time allowed for seeing must be taken into consideration. A small, black-on-gray highway sign requires more illumination than a large, clearly printed black and white sign; and finely detailed articles moving rapidly along an inspection belt must be examined under more intense light than large, crude objects. Studies show that vision improves sharply when low level illumination is increased, even a small amount, but with further increases the improvement becomes slower and eventually levels off. However, this is merely a general finding since the optimal amount of light differs widely from one type of work to another. The following recommended levels take into account both efficiency and comfort, and are based upon widely accepted research performed by Blackwell (1959). Close inspection requires 500 foot-candles; proofreading, 150; general office work,100; wrapping and labeling, 50; dishwashing, 30; loading packages, 20; hotel lobby, 10. (A forty-watt lamp produces about 10 foot-candles on a surface two feet away.) A survey made by Tinker in 1939 revealed that many factories were far below the standard for effective illumination. Many industrial operations were being performed under an average illumination of less than 3 foot-candles—and when the level was raised to 11 foot candles, production was found to increase an average of 15 per cent.Two other considerations are of major importance. First, the general work area should be adequately and uniformly illuminated, and there should be little difference between this levelof illumination and the light that falls on the work object. The second principle is related to this point: lights should be positioned in a way that will minimize glare, since glare spots tend to blind and fatigue the eyes.