Environmental Factors III. The Visual Environment

Abstract

The majority of industrial tasks will depend for their efficiency on adequate vision, and therefore lighting may play an important part in determining the efficiency with which tasks are carried out. Other factors which can also be of importance are the contrasts between the surroundings and the task, which may be influenced by colour, and the presence or absence of glare. To a large extent the recommended levels of illumination which have been current at different periods have depended upon the amount of light which could be obtained economically. The standards of lighting considered adequate in industrial plant 30 years ago would be very low judged by the standards current at the present time; and even as recently as 1958 the standards suggested by the American Illuminating Engineering Society have increased as much as ten-fold some of the standards which were set in 1949 in the U.K. But even now, the levels which can be economically obtained with artificial light do not approach levels which may be obtained by natural daylight under ideal conditions. It is comparatively rare for lighting in a factory in this country to exceed 200 lumens per square foot (lm/ft2) whereas natural north daylight may well exceed 1,000 lm/ft2. On the other hand unless the building is very modern with very large window areas, the daylight factor, that is the amount of daylight falling on the work, is unlikely to exceed 20%, so that under these conditions the levels of artificial illumination are now approaching the levels which are to be found in natural daylight and exceed the levels to be found in the winter or in old-fashioned buildings with very small windows.