There is plenty of evidence that good lighting aids vision and is an economic asset. It should be observed that in most cases good lighting costs no more than bad lighting. If we take into account the harm which bad lighting does to the eyes, it is much more costly than adequate and proper lighting. Eyesight is so important and so easily injured that too much care cannot be exercised in its conservation.
Lighting conditions which cause eyestrain depend somewhat upon the state of adaptation of the eye so it is difficult to define in measurable quantities the limits of these conditions. Excessive brightness, like that of the sun or of modern artificial light-sources, is annoying and harmful to vision. The type of glare due to excessive brightness is blinding for some time after the light-source is out of the field of vision and this temporary blindness has been the cause of many accidents.
1 Adapted from an address before the Eyesight Conservation Council of America. Published by the Council, 1925.
Excessive contrast, which in a sense is similar to the foregoing, causes eyestrain. A brightness which is quite endurable amid light surroundings may be quite discomforting amid dark surroundings. For example, a lighted lantern outdoors on a dark night or a lighted match in a room painted black is quite glaring; while a lighted incandescent lamp when viewed against the bright sky in the daytime is not very glaring.
The light from a wall bracket, which may be viewed with comfort against a light or medium gray wall, is likely to be glaring against a dark background such as dark wallpaper or darkly finished woodwork. Despite this, brackets with frosted lamps are found in many homes installed on a panelled background of dark woodwork or other wall-covering. A decorative fixture which is too bright may be improved by providing denser shades or lamps of lower intensity. In general, fixtures viewed against dark backgrounds are glaring even though the brightness is very low, but this is due to the fact that the contrast is too great. But there is little in favor of dark backgrounds in the home, for they usually contribute toward a depressing effect.
Light may be glaring by virtue of its quantity, but there is a common misconception regarding this. For example, complaints are often heard that artificial lighting is too intense. The intensity of illumination outdoors is usually thousands of times greater than ordinarily encountered in artificial lighting. Commonly, when a room is considered to be over-lighted, the effect is merely glare from exposed light sources. Quantity of light alone is not uncomfortable to vision when the eyes are adapted to the proper level of illumination. When one enters a lighted room after long exposure to darkness the eyes are blinded until they have time to become adapted. Adaptation is an important factor in vision and by this function the eyes are capable of operating satisfactorily throughout a very extensive range of brightnesses or illumination intensities. The brightnesses encountered on a starlit night and those at noon on a sunny summer day represent a range of millions. Under proper conditions the eye will function comfortably throughout this tremendous range of illumination intensities.
Although the sky when viewed outdoors may not be annoying to the eyes, it is not uncommon indoors to find a patch of sky seen through a window to be very glaring. The eyes indoors are adapted to much lower brightnesses than outdoors and the contrast between the patch of sky and the adjacent walls is so great as to be annoying. This is a common cause of eyestrain indoors.
Unshaded light-sources should not be tolerated. Even exposed frosted lamps are glaring under most conditions. Shades should be dense enough to reduce the brightness of the lamps. Even though the bright light source is out of the ordinary field of view, it is annoying when reflected from glossy paper, polished desk tops, blackboards, etc. For this reason light should be emitted from a surface of low brightness. A practical solution is to surround the light-sources with diffusing glass or to diffuse the light by reflection from the ceiling.
Glossy paper is annoying because its smooth surface acts somewhat like a mirror. This is another cause of eyestrain and is contributory to such defects as nearsightedness. Where school children are required to read fine print on glossy paper under glaring or insufficient lighting, nearsightedness increases. The eyes of these young persons are immature and susceptible to permanent defects. In the home these causes of eyestrain should be eliminated before the decorative features of lighting are given attention. The eyes may be misused under any conditions if knowledge and care are not exercised and it is deplorable that such misuse is common.
It is an interesting fact that there is more eyestrain encountered under glaring lighting conditions when the eyes are called upon for near work, such as that of reading, than when they are merely in casual use. For example, in the shade of a building with the eyes unshaded a large expanse of sky may be only slightly glaring. However, as soon as the eyes are concentrated upon a page of reading matter and are engaged in the effort of reading, one becomes conscious of discomfort which in time may become unbearable unless the eyes are shaded. A similar effect may be detected indoors; that is, glaring conditions become much more annoying when the eyes are called upon for their best efforts.
The home and the school are natural and effective places for attacking some of the evils which contribute toward eye trouble. The lighting should be well done; householders and teachers should apply the principles of conserving vision; and in the home-economics courses lighting should be given the attention it deserves.
Although it is not difficult to obtain fixtures which are thoroughly satisfactory from the standpoint of the conservation of vision, there are many in use which are a menace to eyesight. It is easy to state that all lamps should be shaded from the field of view and to add certain facts regarding the correct position in respect to the light-source, but these simple statements do not appear to be effective. This suggests an interesting example of a misconception of art. The bespangled fixtures of the Louis XIV period fitted appropriately the gorgeous splendor of that time. Catering to our weakness - and his own - for copying bygone art instead of creating new styles, the fixture designer reproduces those cut-glass fixtures. As objects, they may be beautiful, and as fixtures used with candles of a few centuries ago they would be delightfully scintillating. However, quite unconscious of the law of appropriateness and of the enormously greater brightnesses of modern light-sources, the architect, decorator, or someone else places our modern lamps amid crystals of glass. The glittering points of light are now a thousand times brighter than they were when this period style was born. They are glaring and unbearable. They are inartistic, despite the fidelity with which their dimensions and details have been copied. Such errors are committed in the name of art, but the result is no longer art.
The lighting problems in the home are not difficult to solve. The subject has been given a great deal of attention by experts and simple directions for various rooms are available.