Artificial Light: Its Influence upon Civilization

by Matthew Luckiesh

BUILDING SHIPS UNDER ARTIFICIAL LIGHT AT HOG ISLAND SHIPYARD

In a certain plant it was determined that the workmen each lost an appreciable part of an hour per day because of inadequate lighting. A properly designed and maintained lighting-system was installed and the saving in the wages previously lost, more than covered the operating-expense of the artificial lighting. Besides really costing the manufacturer less than nothing, the new artificial lighting system was responsible for better products, decreased spoilage, minimized accidents, and generally elevated spirits of the workmen. In some cases it is only necessary to save one minute per hour per workman to offset entirely the cost of lighting. The foregoing and many other examples illustrate the insignificance of the cost of lighting.

The effectiveness of artificial lighting in reducing the cost of living is easily demonstrated by comparing the output of a factory operating on one and two shifts per day respectively. In a well-lighted factory which operated day and night shifts, the cost of adequate lighting was 7 cents per square foot per year. If this factory, operating only in the daytime, were to maintain the same output, it would be necessary to double its size. In order to show the economic value of artificial lighting it is only necessary to compare the cost of lighting with the rental charge of the addition and of its equipment. A fair rental value for plant and equipment is 50 cents per square foot per year; but of course this varies considerably, depending upon the type of plant and the character of the equipment. An investigation showed that this value varies usually between 30 to 70 cents per square foot per year. Using the mean value, 50 cents, it is seen that the rental charge is about seven times the cost of lighting. Furthermore, there is a saving of 43 cents per square foot per year during the night operation by operating the night shift. Of course, this is not strictly true because a depreciation of machinery during the night shift should be allowed for. These fixed charges would average slightly more than half as much in the case of the two-shift factory as in the case of the same output from a factory twice as large but operating only a day shift. Incidentally, the two-shift factory need not be a hardship for the workers, for, if the eight-hour shifts are properly arranged, the worker on the night shift may be in bed by midnight and the objection to a disturbance of ordinary hours of sleep is virtually eliminated.

In a discussion of light and safety presented in another chapter the startling industrial losses due to accidents are shown to be due partially to inadequate or improper lighting. About one fourth of the total number of accidents may be charged to defective lighting. The consumer bears the burden of the support of an unproducing army of idle men. According to some experts an average of about 150,000 men are continuously idle in this country owing to inadequate and improper lighting.

This is an appreciable factor in the cost of living, but the greatest effectiveness of artificial lighting in curtailing costs is to be found in reducing the fixed charges borne by the product through the operation of two shifts and by directly increasing production owing to improved lighting. The standard of artificial-lighting intensity possessed by the average person at the present time is an inheritance from the past. In those days when artificial light was much more costly than at present the tendency naturally was to use just as little light as necessary. That attitude could not have been severely criticized in those early days of artificial lighting, but it is inexcusable to-day. Eyesight and greater safety from accidents are in themselves valuable enough to warrant adequate lighting, but besides these there is the appeal of increased production.

Outdoors on a clear summer day at noon the intensity of daylight illumination at the earth's surface is about 10,000 foot-candles; in other words, it is equal to the illumination on a surface produced by a light-source equivalent to 10,000 candles at a distance of one foot from the surface. This will be recognized as an enormous intensity of illumination. On a cloudy day the intensity of illumination at the earth's surface may be as high as 3000 foot-candles and on a "gloomy" day the illumination at the earth's surface may be 1000 foot-candles. When it is considered that mankind works under artificial light with an intensity of only a few foot-candles, the marvels of the visual apparatus are apparent. But it should be noted that the eyes of the human race evolved under natural light. They have been used to great intensities when called upon for their greatest efforts. The human being is wonderfully adaptive, but it could scarcely be hoped that the eyes could readjust themselves in a few generations to the changed conditions of low-intensity artificial lighting. There is no complaint against the range of intensities to which the eye responds, for in range of sensibility it is superior to any man-made device.

For extremely low brightnesses another set of physiological processes come into play. Based purely upon the physiological laws of vision it seems reasonable to conclude that mankind should not work under artificial illumination as low as has been considered necessary owing to the cost in the past. With this principle of vision as a foundation, experiments have been made with greater intensities of illumination in the industries and elsewhere and increased production has been the result. In a test in a factory where an adequate record of production was in effect it was found that an increase in the intensity of illumination from 4 to 12 foot-candles increased the production in various operations. The lowest increase in production was 8 per cent., the highest was 27 per cent., and the average was 15 per cent. The original lighting in this case was better than that of the typical industrial conditions, so that it seems reasonable to expect a greater increase in production when a change is made from the average inadequate lighting of a factory to a well-designed lighting-system giving a high intensity of illumination.

In another test the production under a poor system of lighting by means of bare lamps on drop-cords was compared with that of an excellent system in which well-designed reflectors were used. The intensity of illumination in the latter case was twenty-five times that of the former and the production was increased in various operations from 30 per cent. for the least increase to 100 per cent. for the greatest increase. Inasmuch as the energy consumption in the latter case was increased seven times and the illumination twenty-five times, it is seen that the increase in intensity of illumination was due largely to the use of proper reflectors and to the general layout of the new lighting-system.

In another case a 10 per cent. increase in production was obtained by increasing the intensity of illumination from 3 foot-candles to about 12 foot-candles. This increase of four times in the intensity of illumination involved an increase in consumption of electrical energy of three times the original amount at an increase in cost equal to 1.2 per cent. of the pay-roll. In another test an increase of 10 per cent. in production was obtained at an increase in cost equal to less than 1 per cent. of the payroll. The efficiency of well-designed lighting installations is illustrated in this case, for the illumination intensity was increased six times by doubling the consumption of electrical energy.

Various other tests could be cited, but these would merely emphasize the same results. However, it may be stated that the factory superintendents involved are convinced that adequate and proper artificial lighting is a great factor in increasing production. Mr. W. A. Durgin, who conducted the tests, has stated that the average result of increasing the intensity of illumination and of properly designing the lighting installations in factories will be at least a 15 per cent. increase in production at an increased cost of not more than 5 per cent. of the pay-roll. This is apparently a conservative statement. When it is considered that generally the cost of lighting is only a fraction of 1 per cent. of the cost of products to the consumer, it is seen that the additional cost of obtaining an increase of 15 per cent. in production is inappreciable.