OFFICE, STORE AND WINDOW LIGHTING BY NORMAN MACBETH The art of applying lighting units to the production of useful and artistic illumination in offices and stores has not kept pace with the development of new illuminants. This is partly due to the remarkable rapidity of this development, and partly to the fact that the later illuminants could not be effectively applied after the completion of the buildings. A great advance in the use of artificial lighting has been made in the past decade. Too often this result has been accompanied with an unnecessary sacrifice in the beauty of the building through the use of inappropriate fixtures or the improper distribution of the light. In resisting this influence architects have sometimes neglected to provide useful illumination in keeping with present-day demands. In such cases the artistic work of the architect has often been undone by the users in the endeavor to meet their practical needs. There are plenty of examples where bare lamps of higher power have been substituted for lower-intensity frosted lamps, to the ruination of the artistic effect and a sacrifice of the physical effect. The cure for this is to provide ample artistic lighting in such a way that it cannot easily be spoiled by the inexperienced. For example, it is often practicable to provide clear lamps concealed in diffusing glassware, tinted if desired to secure a particular color effect. Pressed and blown glass in keeping with the important periods of architecture and decoration are now available, while art glass can readily be made up into any character of design. All modern and efficient illuminants are too brilliant for use without some provision for screening and diffusion. It is necessary to give particular attention to the proper shielding of filaments and mantles of lamps for the protection of our eyes. This shielding, whether with globes, shades, or reflectors, should be done in a pleasing manner so far as the design and general arrangement of the fixtures are concerned. To be able to see clearly and easily is the first step toward efficiency and the amount of energy necessary, while frequently the only previous consideration when speaking of "efficiency" as related to lighting, is secondary. Calculations by the experienced lighting man are largely for a check on his judgment. This judgment is the result of experience on lighting installations and particularly from the results secured from investigations which he personally has made of previous installations. These investigations should always be accompanied with illumination and brightness measurements. While a few years there was very little difference in efficiency between the various sizes of incandescent gas and electric lamps, largely used for office and store lighting, it was a rather general practice to check up these calculations on the basis of cubic feet of gas or watts per square foot. With the wide variation in efficiency of various sizes of lamps at this time, the more simple exact method should be adopted of basing the calculations on the total light output of the lamp in lumens or of lumens per cubic foot of gas per hour, or per watt. It is necessary for good illumination that there should be a sufficiently high intensity, with attention to uniformity, diffusion, eye protection, appearance, and efficiency. The importance of these characteristics of good lighting will vary in different installations. Efficiency has at times been given too much attention and prominence. It is used here to refer in office, store or window lighting to that proportion of the generated light effective on an assumed plane. At times this consideration is extremely important, and at other times of practically no importance. It is necessary, of course, for the predetermining of results, to know the probable efficiency of the installation, that is, what per cent. of the total light produced by the lamps reaches the working plane. This is generally termed "utilization efficiency" and may vary from 70 per cent. to 10 per cent. or less of the total light from the lamps. It is possible to design a lighting installation which from this single standard would have a high value, but which, from the standpoint of assistance to easy and clear vision, that is, from the standpoint of good illumination, would be an absolute failure. Within the past few years there has grown up a strong appreciation of the ill effects of bright sources on the eye and of extremes of contrast between the average brightest and darkest portions of the room. There is a tremendous difference nevertheless between equipment which without photometric tests appears to be quite similar but which, from the standpoint of distribution of light and the contrast conditions set up, may vary in efficiency upward to 50 per cent. Indirect lighting or semi-indirect lighting in which no part of the fixture is brighter than the ceiling is generally more satisfactory than the average system of direct lighting where clerical work is done, as tests have shown that the efficiency of the eye is reduced very rapidly under any system of illumination in which light sources of a brilliancy of those of our commercial types are within the ordinary range of the eye. Much of the so-called semi-indirect lighting is but slightly modified direct lighting. This kind of lighting with light density glassware has been most general and has undoubtedly resulted in the unjust condemnation of semi-indirect lighting as a whole. It has been shown,1 however, that of the glassware on the market used for semi-indirect lighting fixtures, at least 90 per cent. of it has too high a transmission. A worthy endeavor is being made to reduce this contrast in lighting installations to within the range of 100 to 1, that is, the brightest object within the range of view should not be more than 100 times brighter than the average lower intensity. The average. semi-indirect lighting installation with light density opal glass is merely an inefficient system of direct lighting. In many locations direct lighting, particularly where the ceilings are low, would better meet the requirements. In all such cases, however, very deep bowl glass reflectors having low transmission should be used. The lamp filament should be covered down to the 65° point, and it is also desirable that the lower edge of the reflector be flared out so that this part of the reflector interior as ordinarily seen be not overly bright. There is an important difference between diffusion of light and diffusion of illumination.2 Light from a single source, no matter to what extent that light may be diffused by the enclosing media would, from the standpoint of illumination on a desk, not result in diffusion. Diffusion of illumination is the important factor and is the result you secure when the light received on the surface viewed is from a number of directions. This may be secured through close spacing of units or through using the ceiling as the light distributor either with indirect or semi-indirect fixtures. Good diffusion of illumination is essential in offices, drafting rooms and similar places where glazed paper or desk tops with polished surfaces are in use. For stores, a high degree of diffusion is not so necessary and is generally present to a sufficient degree with any system of lighting because of the large number of outlets. Maintenance of lighting equipment should not be overlooked and it is very important that arrangements be made for a proper cleaning of the equipment at periods varying from two weeks to a month or more, depending upon the dust conditions of the location. Deterioration is less with direct lighting reflector and lamp units than with the indirect or semi-indirect units. There are locations where it would not be possible to keep indirect and semi-indirect units clean without a cleaning period so frequent as to be unnecessarily expensive. In these cases direct lighting equipment will permit of longer periods between cleaning. It is well to remember in accepting tables of desired intensity, utilization factors or constants, and methods of calculation generally furnished by the equipment manufacturers that these values are invariably for new clean equipment. An average deterioration factor should be used of 10 per cent. to 25 per cent., depending upon whether the maintenance is likely to be good or average. In considering fixture design, it is worth while to note also the ease or difficulty as the case may be with which the equipment can be cleaned. Fixtures should be substantial and the means of removing glassware for cleaning should be simple. Ordinary labor is generally used for maintenance and holders with springs or similar complications are not easily taken care of by the average cleaner. OFFICE LIGHTING Office employees as a class are subjected to more severe eye-strain than almost any other class of workers. In our large cities during many hours of the day and in many instances all day, they work with a mixture of natural and artificial light. The intensities of the latter, in these days of unwise economy of energy for lighting, are rarely adequate. There would seem to be little doubt that with a mixture of daylight and artificial light, a higher intensity of artificial light is required than where artificial light alone is used. Whether this is due to a higher eye adaptation demand or to color differences, has not been decided. The frequent use of an instrument for measuring illumination intensities cannot be too strongly recommended. In a recent installation complaint was made that the clerks were having difficulty with their eyes, although apparently the lighting installation had been given every possible design and maintenance attention. On inspection it was shown that the spacing and kind of fixtures were satisfactory, the contrast between the brightest and darkest object in the room was well within the proper range and the installation had every appearance of being right. Illumination measurements, however, brought out the point that the average intensity was about 1.5 foot-candles which was certainly not high enough for the character of clerical work performed. A simple increase in the size of lamps used corrected the difficulty. In a recent investigation3 in a block of office buildings in New York City, over 85 per cent. of the workers were under artificial light or a mixture of natural and artificial light all day, and over 90 per cent. of them worked more than eight hours per day. Some of the clerks and stenographers had only 0.5 to 1.5 foot-candles on their work. Others again by the use of portables, mostly placed improperly, worked under 30 to 40 foot-candles, likewise suffering from headaches and eye discomfort. An entire floor of ledger keepers with a system of semi-indirect units, otherwise satisfactory, had only 0.5 to under 2 foot-candles effective at the desks. The misdirected economy demands of the office building superintendents or the competition demands of the venders of lighting equipment, to do with a less energy expenditure than necessary, was undoubtedly accountable for these installations. Economy is frequently referred to in considering office lighting. The economy which is most lasting, however, is that which avoids the waste of human energy.^ "Such waste has no compensating return but is an irretrievable and total loss. The man who works an entire day to accomplish that which, under obtainable conditions, he could accomplish in half a day, has wasted a portion of that which is above all price-life. ficient light is indefensible from every standpoint vital of all economies is the saving of human energy Poor and insuf- not overlook the fact that we work by sight, that we see by light." Let us In discussing the cost of lighting, Professor Charles F. Scott stated that in one instance the cost of good light for an office was but 2 per cent. of the wages; that "the difference in cost between good light and poor light would be 1 per cent. of the wages," noting that "One per cent. of an office day was about five minutes, that if clerical work can be done with greater ease and figures read more accurately, if there is greater rapidity and fewer errors, if there is less eye strain, less headache, greater comfort and satisfaction, so that more and better work is done in eight hours than would be done in eight hours and five minutes with a poor light, then the extra cost is justified." It was also shown that the difference in cost of equipment between |