EXTERIOR lighting involves problems of a quantitative character, whereas interior illumination is more qualitative, and while both are important, the successful solution of the interior problems has perhaps the greater practical value; for it is obvious that while indoors our eyes are subjected to greater stress, Apparently there is no reliable and clearly defined record which will guide us in providing both natural and artificial conditions of illumination closely corresponding to those under wheh the eye is most capable of rendering its best service. At least an exhaustive search, in connection with which the writer has assisted, failed to produce any real data or indication of previous thorough and logical analysis, and consequently, in undertaking the illumination problem of an important exhibition picture gallery recently erected, it became necessary to inspect many of the existing buildings of similar nature, after which it was deemed advisable to approach the problem on entirely new lines. While this article, therefore, will be confined largely to a description of the solution of the particular problem undertaken, there. is much information brought out in the analysis that applies directly to the illumination of almost any kind of an interior, the principles, of course, being observed, rather than the exact arrangement or construction. Quite to the writer's astonishment, no one seemed to possess the key to the whole situation, although many persons who were interviewed seemed to appreciate, in a rough way, the defects noted in the existing buildings. Daylight illumination has received a good deal of study in reference to special interior problems, but the records do not show that these investigations have been carried sufficiently far for us to learn from them the intensity of illumination that pictures, for example, should receive, or the best relative intensities for the various fixed surfaces, ceiling, walls and floor, of a given robm. Incomplete as were the daylight experiment data, the results from previous attempts to provide scientifically correct artificial lighting proved to be even more unsatisfactory. Before enumerating several of the violations most frequently committed, I will mention briefly a few of the principles governing the subject of light and its effect upOn the human eye. Through many ages, the human eye has accumulated the characters wrought upon it by evolution and the limitations of its environment. It works best over a rather limited retinal area and through a range in intensity of light which, although great, is yet much smaller than, for example, the extreme variations in brilliancy provided by the sun's rays. Everyone is familiar with the distress caused the eye by sudden alternations of light and darkness, and it seems to be well established that the discomfort caused by the reflected glare from sand, water or snow is due to the inability of the rather transparent lower eyelid to obstruct sufficiently the light that approaches the eye in an upward direction, a condition to which the human eye is not naturally accustomed. All these matters are of importance to consider in connection with interior lighting, and the subject of the following serves as an excellent illustration. Visitors view pictures to study their relative merits, and are often so absorbed in this, as not to realize, until afterward, under what trying conditions their Fig. 3.—Lighting that does more harm than good. eyes have been used. The lighting of a picture gallery or exhibition room differs from other interior illuminating problems, but the underlying principles may, nevertheless, be otherwise applied when they are once appreciated. First, the main objective is to provide an illumination which will enable persons to view exhibits with the least possible discomfort or effort to the eye; second, the exhibits will be on the walls and, therefore, the light must be directed there; it, however, must be diffused; third, should the floor be especially bright, or the source of illumination in the field of vision, there is a physiological effect exerted upon the eye which makes. the. careful viewing of objects not only difficult, hut most tiring. The most suitable intensity of light and the seemingly contradictory requirements that it must be both directed and diffused are difficult conditions to establish, but it is obvious that in every picture gallery or exhibition room the need for solving these essential points has been felt. How frequently do we see the gallery skylight provided with a roller shade or an opaque canopy placed in the center of the room, under which observers may stand to view the pictures without exposure to the direct effects of the. entering light. These are but makeshift methods of regulating the intensity, and by negative means, directing the light. Until most recently, however, these devices were regarded as essential features of gallery equipment. An interesting feature of this situation was, that the results desired, as indicated by these makeshifts, were quite correct, for as one eminent critic described the situation, “the best results would be. obtained F in some way the direct rays of the sun's light could be shut out, but the remainder of the daylight be admitted through an overhead skylight, and each visitor be provided with an open umbrella to hold over his head while viewing the pictures.” This was the remark of an artist whose knowledge of science and physics was limited to his original observations, but his expressed idea conveyed to the writer that the full range of the sun's brilliancy was vastly too great, and its effect should be modified to correspond more nearly with the limitations of the human eye, and the largest portion of the entering light should be directed toward the walls and not allowed to fall directly on the floor, as is generally the case, where the hung canopy is not used. The canopy, however, is not a desirable intrusion at best, but it is often used to obstruct the downward flood of light, which is sure to enter when the sun is high and the surface of the glass area is entirely skyward, a mistake in roof design heretofore almost universally made. It is, nevertheless, a fact that in spite of its unsanitary objections and unsightly appearance, from a lighting standpoint, the presence of the hung canopy is to be preferred in galleries or exhibition halls where the skylight is so constructed. Hence, the manner in which the light is admitted is all important. The area of the glass opening in the gallery ceiling governs the amount of light that can be admitted, but the shape of the superstructure. or upper skyklight practically determines the manner in which the light “ghall enter. Although well above the room in which the exhibits shall be, this “superstructure” should be most carefully designed. Its top must be opaque so (ConMnueiZ on page 397.)
This article was originally published with the title "Indoor Lighting, Natural and Artificial"