Document V36aJJbn4nqG4xk2K2m3yxmXK

780 S. K. GUTH AND E. A. LINSDAY area cleaning at least twice per year is recommended,89 but this varies widefe depending on the rate of dirt accumulation and the type of lighting system in stalled. Figure 28 shows some typical conditions. Relamping is done either on an individual replacement basis or on a grdf| replacement plan.65,60 With the consistent lamp life characteristic of present-c(i| sources, the group replacement plan is usually the more economical. Lamps*! replaced at 70 to 80 per cent rated life, and the few burnouts between replaceiifi schedules can be replaced individually with the best of the operable lamps fromiM previous group. Group relamping may be done during .a cleaning operation further cut costs. Under the group relamping plan the small additional cosffli lamps is offset by the reduction in labor cost of doing the job on a mass-producmgj basis. X. Supplementary Lighting In many applications the general lighting, system alone is not sufficient, "Sk! some kind of supplementary lighting01-03 is necessary (Figure 29). It mus||||f kept in mind that supplementary lighting is just what the word implies--ligfi|| that supplements the general lighting system, A good general lighting system|| still necessary to provide an over-all comfortable seeing environment. Wh'e^S object or task is small in size or has little contrast with its immediate back^^CT an additional quantity of light supplied by a supplementary system increas^P worker's seeing ability. For these tasks a well-shielded source directed s|^P work is employed^-- Directional lighting is often used for detecting scratches, pits, and Jjul flaws on nonspecular materials (Figure 30). For this purpose a be&m'fralMj provided by narrow-beam reflectors, lenses, or spot lamps is directed atjaigl^S angle across the surface of the material being inspected. Defects will s$ov|f|i highlights or shadows. This method may sometimes be used also on spt materials. The surface to be inspected appears dark to the operator,;^exqiB imperfections, which appear bright because they reflect light. One must.iiS^ ticularly careful to control the directional beam of light so that it is slueJSIPL the operator's eyes and from other persons. .]S A third technique employs a diffuse light source, generally large m-arjjifi .... . '"""CrEr'Egeler ancI*'RTFrValicletiB&9iK7 Maitit6ffailc6"5ri`5'dil3tTial"H'gKtmg-- m' " Eng., 48, 631 (1953). .... ....... " i` 00 Lighting maintenance--group relamping, Bulletin LS-155, Lamp Division"JGerierix Electric Co., December, 1953. 01 Recommended practice for supplementary lighting (Prepared by the Subcomffi|fi -OP_SupplemBtttaiydUghtmg-QtAheJCaiMnildaecmiilaglitingtcStudyjEmiectsrmrJflgult'q Illuminating Engineering Society), Ilium. Eng., 47, 623 (1952). |llp,,-aM *C. M. Cutler and E. A. Linsday, Supplementary lighting, Magazine of Eigf,r.:2O^0 (November, 1951). ' "E. A. Linsday, Specialized lighting for inspection and control, Ind. Quality ,'Qaz 11, 357 (1954). 7 % , y-avA LIGHTING FOR .SEEING <7SS?arcenR>>**3 'C&*\* i-Jc.'M zmm 781 UUre 30' Venetian 'bbi7'laf^|h?Fiif"Sy detected %a beam of lig^^Ureete|jag;ai88itg^S^0e acro^. th'esutf^ face roughness is;.not:as'apliarpnt);'gRg,.j^:> = >,. A,r in brightness, for illuminating the material to.be:Unspee;ted.:(F>igures,:-31 ^^ may '^e use^ for transilluminating materials- suchias-hphbfcogra:{)hic;! neSflyes: bottles* and fabrios for inspection purposes (Figure 33).t\. Diffused i^ces with a pattern of lines painted on the translucent panel are used to.-d'etec);