Document wq4jGr2bVM0Y48kjZgbb83mXd

86 ROSS A. MC FARLAND objects (a lamp filament, for example), localized brilliant lighting by means of a special fixture can be used to "magnify" the work. Listed in Table 4 are some representative visual tasks and current recommendations believed to provide TABLE 4 Recommended Illumination for Various Types of Tasks"'" Tasks comparable to Recommended illumination (footcandles) Reading legible print (10 point) Sorting, rough inspecting, bookkeeping, reading newsprint Setting 6-point type, stitching, gross assembly work Severe industrial tasks, such as fine inspection, engraving, grading and sorting, proofreading 10-16 16-20 30-40 40-60 adequate levels of illumination (Cf. Chapter XX). For persons who have some slight eye disabilities or those with corrections, the lower levels in the table can be increased by 5 to 10 footcandles.42 An increase in the illumination may be beneficial to persons in the older age groups. A number of devices are available for measuring illumination of the working area and its surrounding environment. Some of these depend on visual matching (for example, the Macbeth illuminometer), whereas others operate entirely on physical principles (for example, photocells of various types). When any type:of photometer-is-used--it-is-important'-to-remember-that-the-illumin&tion..measur< ment should be made at the place at which the eyes look and not at the lighting fixtures that produce the illumination. e. Time of Exposure. Many industrial jobs may not be affected by this vari able, since the employee ordinarily can control the rate of his operations. In some jobs, however, such as high-speed assembly-line work or vehicle driving, the opera tor must obtain visual information very quickly. In these cases, there may not be time to detect the necessary information.48 Fortunately, however, a drop in expo sure time may be in part compensated for by increasing the illuihination. Some of the other factors already listed also can be used instead of, or in conjunction with, illumination to overcome the loss of visual perception due to short exposure. Thus, -one-can-increase-th6-8ize-of-the-v-i8ual-detail,-raise-theiilluininatiOn'Sinciease_the__| contrast,::or:decrease the glare when a fast operation.'dependB'bBithejuse: of ;the eyes. Whenever feasible, each variable should be Used fodt^fuliest' extent. When this is impossible (as when time is short or the size of the visual detail is dictated by the.iOperationJts.elf), it should be recognized that other factors are available and can be utilized to create a more satisfactory visual display.2 "M. A. Tinker, Trends in illumination standards, Ilium. Eng., 43, 886-891 (1948). "J. E. Kuntz and R. B. Sleight, Effect of target brightness on normal and subnormal visual acuity, J. Applied Psychol., 33, No. 1, 83-91 (1949). "P. M. Fitts and R. E. Jones, Psychological aspects of instrument display: I. Analysis of 270 "pilot error" experiences in reading and interpreting aircraft instruments, AMC MR TSEAA-694-1SA, October 1, 1947. HUMAN ENGINEERING AND INDUSTRIAL SAFETY 87 WS*"1 ' Color oj Illumination. The use of color should be considered with reference few ^"itofbp.th normal and color-defective vision. Although the figures usually cited show as many as 5 per cent of the male population are color-blind, recent estimates ndicate that as high as 16 per cent of males may be "color-weak." The incidence jHcolor blindness in females is much less. Many accessory visual aids, such as ^-^mapsV'charts, signB, and posters which have color designs, are unintelligible to m r.|blind..i.n..d..iv..i.d.u..a..ls and sometimes may be confusing even to the color-normal, a recent years, color has been used as an illuminant in incandescent or fluores'^j^eiit.-fiitures and colored paints have been used for bench surfaces, walls, working ^wmaterials, tools, and machines. It is necessary to distinguish among the purposes fir^-i'n"diiifjyehintCeorelosrt iiss ounselydthinatthoebsjeecvtsamrioauysbceirsceuemn setaanscileysa. nIdncosommfoertianbstlayn. cIens,otthheer Iinstances, color is used as a code or symbol to signify a particular bit of informa tion (red for danger areas, green for electrical connections, black for tool handles, anjl.so forth). In cases where colored lights are used as warnings, it is obviously important that the most easily discriminable colors be used. For viewing colored' # , jraiiitsiof light, it has been shown that red, green, and blue are the most easily l._niz*ed, followed by white and yellow.44 S T*ay evaiuating the effects of color is to compare the effectiveness of ^^fij^cjuomati'c contrasts (such as black objects on a grey surface) with chromatic i;'"'- * / i (such as green objects on a yellow background). Most studies have tiyShriwn.lhatfechr.omatic-contraat-ia,a..more-powerful.factor than chromatic contrast ,i^un|iprpdiising discriminable effects.48 In fact, the increased visibility that one the use of colors often can be attributed to the difference in bright- (achromatic contrast) between the colors rather than to the difference in j^^w'5)|jju?, for maximal visibility, black on white or vice versa seems to be the arrangement, although black and yellow have also been shown to produce iw&Mi&coo^ragt. S. Types of Visual Displays 'il*;' 'r. 4KfPPV'Analysis of the different ways in which workers use visual displays indicates .|1^T ifemafebe a warning signal (such as a green light to show things are normal, 1 iferto.show danger or faulty operation). This is calle^ascheck display. ^5^tB^t\fi.,:o'nn~typfi,.oLrequir.ed.information is whether, and in which direction, a chase Wit abjiqfie|aiti0n has departed from normal. Many dials showing revolutions, tem- . Since under normal working condicertain range, it is possible to cover up light signals which are near the limit of SM&Pfiy*. Soc. (London), 59, 56<74 (1947). t SWfiUAill1 B alitahVmn1y1 afinnJd 8a. XM/. VNTultwrhLaH 1l1l, AA tiitnrUibautive- 1li1m e_n_s in selected regions of the MUnsell : ftfe 'J ^igohd.sj. Opt. Soc. Amer., 32, 465-473 (1942)