Document dnZqJbR7G4qpGRMwOeNz99j8e

754 S. K. GUTH AND E. A. LINSDAY substantiate these results. Investigations have shown that these brightness re tionships between a task and its surroundings are of greatest importance wit about a 60-degree zone around the line of vision. Another cause of visual impairment and discomfort is the brightness of m remote areas such as lighting equipments. Extensive investigations83-36 h shown that large areas of even apparently moderate brightnesses are disturb and produce discomfort even when located at considerable angular distances f the normal line of vision. Factors such as size, position, and brightness of sou and the adaptation or field brightness, all are important. In Figure 8 are illustra BCD IS MAINTAINED BY BALANCING BRIGHTNESS VISUAL SI2LE SOURCE POSITION . .. -Mr, . \THE FIGURES ABOVE THE CIRCLES REPRESENT RELATIVE BRIGHTNESS s THE FIGURES WITHIN THE CIRCLES REPRESENT RELATIVE AREAS brightness ;:,TM MULTIPLYING FACTORS FOR OTHER UK ADAPTATION LEVEL* ADAPTATION BRlGHWE .BRIGHTNESS-----,-EASg? 10 I, 20 1.16 30 lj 40 LB 50 2 Figure 8. The relative effects of size, brightness and location of a source of brightness! visual comfort (BCD = borderline between comfort-and discomfort). the relative effects of these factors and how they must be balanced so thrift work area will be visually comfortable. When sources of brightness are lpt^ near the line of vision (indicated by the horizontal line), they must be smal size or low in brightness. As they are moved farther from the task area, step -brightness-may-be-increased--fts-shown-by-the-values-in-and-above-th^cirl^ combined effects are shown by the circles on the broken line, which is for|S ^ stant position index.36 In order to maintain a constant visual sensation-ks-all " M. Luckiesh and S. K. Guth, Brightnesses in visual field at borderline between' e| and discomfort (BCD). Ilium. Ena., 44, 660 (1949). ' "S. K. Guth, BCD brightness ratings in lighting practice, /Hum. Eng., 47, 184 "P. Petherbridge and R. G. Hopkinson, Discomfort glare and the lighting of .W.|mfi Trans. Ilium. Eng. Sac. {London), IS, 39 (1950). ^ " Position index is an indicator of how much the brightness of a source may be Inigg^ as it is moved from the line of vision in order to maintain a constant visual Bensation. LIGHTING FOR SEEING 755 reased from relative values of 1 to 27, relative brightness must be reduced ..ffieaaivelv from 355 to 100. For larger areas, the brightness must be decreased iffgven greater rate. The table in the lower right comer of Figure 8 illustrates wphe source brightness may be increased for higher adaptation brightnesses. lif adaptation brightness is doubled (corresponding to a doubling of the llandle level) the source brightness may. be increased 'by only one third, ds have been proposed for evaluating the comfort of lighting systems and ing used for design purposes.37 eeing is a dynamic activity of human beings. Since a worker may look at 1 rt of a visual environment, it is important to eliminate extremes of bright-r darkness. If they are not eliminated, the worker's eyes must continually pting to a greatly changing brightness pattern. Fatigue and ease of seeing 8 have shown that, pupil diameter^8 precision and rate of working,811 and rate80 are adversely affected by improper brightness relationships. V. Color he subject of light and color40 is large and complex. However, it is not as erious as some people try to make it. While spectral quality of light is im- ant in some visual situations, it is generally of secondary importance in and seeing. So-called white light ranges from a yellowish white with -filament lamps to a bluish, white with1 daylight fluorescent lamps. All of : suitable for general lighting use. No real, practical advantage has been jatft(Lfcm.any_one_.ov,er.another..-Foot'cahdle4e.ye;i~and brightness are of, jiipunt importance. j|fbr specialized tasks involving color discrimination, lamps emitting all colors ^be used. A wide range of fluorescent lamps now is available. Those designated jluxe provide balanced spectrums and have been found.completely satisfac- Jdr color-critical work. For other tasks, relatively saturated color of light "" i used to enhance the contrast within the task. In such|eases the golor of, the !Jhould be complementary to .the surface color. Bblor of light also is useful for creating a warm or cppli^riiosphere. This, has I to be particularly desirable to help cpunteract^the.-effects. of' hot or .Industrial operations-and to cfeate a'ffiltire livable envirdhihent. ... (. .. ------ . , . VIv TlielHnman. Eleinent researches in seeing must 'of necessity involve the human element. How- ,,-pin most cases differences.;,among individuals, are. submergedlri averages. y=-R=sMeaker-and--Rrfe -Qafattmgz3SffllihcQiM^ ''. lighting'design, Bulletin LS-108, Lamp Division, General Electric Co, October, 1953. Luckiesh and F. K. Moss, Size of pupil as a possible index of ocular fatigue, dm. J. %&imol., 16, 393 (1933). ||M. Luckiesh and F. K. Moss, The rate of working on alternating fields of different nesses, J. Franklin /nst., 200, 731 (1925). 'A. H. Taylor, The nature and causes of small color differences in industry, J. Opt. Soc. 132, 651 (1942).