JrxK 1. I9J1 



THE INDIA RUBBER WORLD 



641 



greatest inecliaiiical crticieiicy of lighting is to be obtained, that is, 

 tlic minimum amount of hght used, the machines must be arranged 

 with reference to the liglit-units. Thus in the case of the machines 

 just referred to, they must be set so that one unit will light one 

 side each of two machines. Similarly, tire-building stands may be 

 set in rows so tliat the operatives face each other with the light- 

 units hung over the aisle, thus giving the desired fi-ont light free 

 from shadows. 



To set a machine with reference to a lamp may seem at first a 

 case of the tail wagging the dog, but a moment's consideration 

 will reveal the simple fact that it is .lust as easy to set a machine 

 so as to permit the most efficient lighting as in any other way. 

 Such a system will more frequently contribute to economy ot 

 installation and oiK-ration than otherwise. 



IMPORTANCE OF DIRECTED LIGHT 



The problem of shadows is a matter vi the direction of the 

 light and the size of the luminous source — the larger the source 

 the smaller and less distinct the shadows. The mercury-vapor 

 lamp vvitii its luminous tube four feet long presents a correspond- 

 ing advantage over the incandescent units, which are relatively 

 small. Add to this the greater visual effect of green light at the 

 lower intensities — which constitutes shadows — and the shadow- 

 problem is pretty nearly eliminated by the use of these units. In 

 the case of small machines set close together a good intensity — 

 not less than 10 foot-candles — of general illumination by C-H 

 lamps will usually afford the best solution of the prolilem. 



There are many cases in which a strong directional light is 

 essential to the most efficient vision. Thus, fabrics show their 

 texture much more distinctly when illuminated by a strong light 

 from one side. Air bubbles in tires show up plainer by side light 

 than by "end-on" light. In all cases where small differences in 

 the surface must be observed side light should be used. This 

 applies particularly to inspection. 



Bench and table lighting is the same general prolilem, irrespec- 

 tive of the work done, and is the simplest of all problems to solve. 

 Where possible the benches should be double, that is, the oper- 

 atives working on each side, so that units placed above give an 

 unobstructed light to all. The practice of placing benches along 

 the side of a room in front of the windows is open to serious 

 criticism, and is a relic of the days when daylight afforded the 

 only illumination by which fine work could be done. In modern 

 mill construction with the large area of window space, benches 

 at right angles to the windows are better for both natural and 

 artificial light. 



Room lighting is now about as simple a proposition as bench 

 lighting. As we have pointed out before, the law of the survival 

 of the fittest, operating in the development of electric lainps, has 

 reduced the units available for industrial use to two types ; the 

 mercury-vapor lamp and the gas-filled tungsten lamp, bowl frosted 

 or enameled, and fitted with a white enameled steel reflector. 

 Tliese give the same distribution of light, and all the necessary 

 calculations can be made by the use of a little simple arithmetic 

 with the assistance of the distribution curves furnished by the 

 manufacturers, as previously explained. With proper room, bench, 

 or machine lighting, the use of drop-lights is practically eliminated 

 — which is good riddance tn an old-time nuisance. 



WIRING FOR A FLEXIBLE SYSTEM OF LIGHTING 



But suppose you "light the job," that is, place the units with 

 reference to the machines, and later rearrange the machines, or 

 use the space for other purposes : will not this require a re- 

 arrangement of the light-units, necessitating more or less rewiring? 

 It undoubtedly will. That is part of the cost of improvements due 

 to the general progress in the art, or to faulty engineering, or 

 lack of engineering at the start. 



In the case of a building or room specially designed for the 

 operation of certain kinds of machines, the chance that it will 

 be used for other purposes, or that the character of the machines 

 will be radically changed in the near future is sufficiently small 



to justify a single system of wiring to supply the light-units de- 

 cided upon. But in a room that is equally well suited to any of 

 the machinery or processes used in the production of the general 

 line of rubber goods, and which may, therefore, be utilized for 

 different purposes in the growth of the plant, it is manifestly 

 better engineering to provide a sufficient number of outlets with 

 their corresponding switches and fuse blocks, to enable light-units 

 to be installed at any point desired with a minimum of special 

 wiring. This, of course, refers to new buildings. 



A very practical arrangeincnt of this kind, which is being used 

 by one of tlie most progressive rubber manufacturers, is to run 

 two rows of outlets down each row of bays, the outlets being 

 "staggered" so as to give three in each bay. Tlie outlet consists 

 of the female half of a plug inserted permanently in the cement 

 ceiling. The light-units are then placed with reference to the 

 illumination desired, connected to the nearest outlet, and con- 

 trolled by pendent swilclies. 



THE MECHANICAL EFFICIENCY OF THE LIGHTING SYSTEM 



There now remains to be considered only the question of the 

 mechanical efficiency of the lighting system as a whole. As in all 

 the other calculations with reference to illumination, rigid exact- 

 ness is impossible, and we must be satisfied with more or less 

 close approximations. 



As in the case of any other mechanical equipment, the cost may 

 be considered under two general heads, namely, fixed charges, and 

 maintenance. In the present case fixed charges will include in- 

 terest on the original investment and depreciation (amortization). 

 Maintenance will include cost of electric current and repairs or 

 renewals. For the purpose of comparison let us assume that the 

 lighting installation will be operated 3,000 hours a year. In the 

 two available systems, the mercury-vapor and incandescent, there 

 are no two units which are exactly comparable in respect to light 

 produced or current consumed, so the better method will be to 

 take the nearest alternatives and then reduce the results to a 

 common basis— say of 1,000 lumens of light for a year of 3,000 

 hours. We will, therefore, take the standard mercury-vapor lamp 

 having a SO-inch tube and white reflector, and using 430 watts of 

 current, and the incandescent unit consisting of bowl frosted gas- 

 filled tungsten lamp equipped with the standard R. L. M. reflectors, 

 using 400 watts. The mechanical efficiencies of the units, as given 

 liy the manufacturers, is as follows : 



TJnit Current Tital lumens Lumens per wall 



Jlercury. vapor 430 6,\29 14.2 



hicandescent, 400-\vatt 400 4,350 lo!9 



The total operative cost by these several units for a year, and 



3,000 hours' use, will be : 



Mercury. Incandescent 



X'.-Iior 4llll-\Vatt 



rirst cost of ])ermanent parts $J2.S5 $3.21 



I uteres* at 6 per cent en first cost 1.37 '.I9 



Deprecirili-m at 12 v-, per cent 2.85 .40 



Renewals 4. 50 9.45 



Current at 1 cent per kilowatt -liour 12.90 12.00 



Total oper.ltive cost $21.62 $22.04 



Ojierativc cost per 1,000 Inmens $3.53 $5.07 



In the above table the cost of lamps is figured on an average 

 quantity discount. Maximum and minimum discounts would make 

 a difference of about 25 cents and 60 cents per 1,000 Itunens, re- 

 spectively. 



The figures are also based upon initial performance. Tlie de- 

 preciation in candle-power by photometer measurement may be 

 somewhat greater with the mercury-vapor than with the tungsten 

 lamps ; but the results of the psychophysical experiments, which 

 accord with general experience, show that any difference of this 

 kind is much more than offset by the higher visual value of mer- 

 cury-vapor light. 



The cost of renewals is based upon a guaranteed life of the 

 mercury-vapor tube, three years, and the estimated life of the 

 tungsten lamp, 1,000 hours. 



From the cost per lumen it is very easy to figure the cost for 



