That it should be possible to do close work under illuminations so fantastically low compared with those which are met with out of doors in daytime is a remarkable tribute to the native endurance and flexibility of the sensing eyes and the perceiving mind. So great is this flexibility and endurance that a person whose eyes are unimpaired, and who uses them in the way that nature intended them to be used, can submit for long periods to bad lighting conditions and suffer no harm. But for a person whose eyes have undergone some organic impairment, or whose habitual functioning is so unnatural that he can only see with effort and under strain, these same conditions may be disastrous.
In his book, Seeing and Human Welfare, Dr. Luckiesh has described some very interesting experiments, which demonstrate the undesirable consequences of poor lighting. These experiments were designed to measure nervous muscular tension (an accurate indicator, as Dr. Luckiesh points out, of “strain, fatigue, wasted effort and internal losses”) under varying conditions of illumination. The task assigned to the subjects of these experiments was reading; and the amount of nervous muscular strain was recorded by a device which measured the pressure exerted by two fingers of the left hand resting upon a large flat knob. The subjects were kept unaware of the nature and purpose of the investigation—indeed, were deliberately thrown on a wrong scent. This eliminated the possibility of any conscious or voluntary interference with the results.
A very large number of tests showed conclusively that, in all cases, “there was a large decrease in nervous muscular tension as the intensity increased from one to one hundred foot-candles. The latter was the highest intensity investigated, because this is far above prevailing levels of illumination in the artificial world. There was impressive evidence that this tension would continue to decrease if the level of illumination were increased to 1000 foot-candles.” In other tests the subjects were exposed to improperly placed lights that threw a glare in their eyes. This glare was not excessive—just the average, moderate glare that millions of human beings habitually work and play by. Nevertheless it was quite sufficient to increase the tell-tale nervous muscular tension to a marked degree.
There is, so far as I know, only one kind of electric light bulb from which one can obtain a thousand foot-candles of illumination without excessive consumption of current. That is the 150-watt spot-light, described in the chapter on sunning. The parabolic and silvered back of this bulb acts as a reflector, and the light issues in a powerful beam, in which reading, sewing and other tasks requiring close attention and precise seeing can be performed in the best possible conditions.
During the daytime, people with defective sight should always make use of the best illumination available. Whenever possible, close work should be done near a window or out of doors. I myself have derived great benefit from reading for long periods at a stretch in full sunlight, either falling directly on the page, or, if the weather was too hot, reflected by means of an adjustable mirror, so that it was possible to sit in the shade, or indoors, and to enjoy the advantage of seven or eight thousand foot-candles upon the book. For some months, indeed, after giving up the wearing of spectacles, it was only in full sunlight, or under a spot-lamp, that I could read comfortably for any length of time. But as vision improved, it became possible for me to make use of less intense illuminations. I still, however, prefer the spot-light to all others, and frequently work in full sunlight.
When reading in full sunlight, it is necessary to keep the eyes thoroughly relaxed by means of periodical brief sunnings and palmings. Many people will also find it easier to read if they make use of a slot cut in black paper, as described in an earlier chapter. When these precautions are taken, reading under ten thousand foot-candles can be very helpful to those whose vision is defective. Falling upon the center of sight, the image of the intensely illuminated print stimulates a macula which has become sluggish and insensitive through habitual wrong use of the organs of seeing. At the same time, the clarity and distinctness of the sunlit letters exercise a most wholesome influence upon the mind, which loses its habitual strained anxiety about seeing and acquires instead an easy confidence in its ability to interpret the sensa brought to it by the eyes. Thanks to this confidence and to the stimulation of the sluggish macula, it becomes possible, after a time, to do one’s seeing no less effectively under lower intensities of illumination. Ten thousand foot-candle reading is a preparation and an education for hundred foot-candle reading.
Owing sometimes to organic defects of the eyes, sometimes to ingrained habits of improper functioning, sometimes to generalized ill-health, certain persons are peculiarly sensitive to intense light. For these it would be unwise to plunge directly into ten thousand foot-candle reading. Following the techniques described in the chapter on sunning, they should gradually accustom themselves to tolerate greater and greater intensities of illumination, not only directly on the closed and open eyes, but also on the printed page before them. In this way, they will come by slow degrees to be able to enjoy the advantages of good lighting—advantages from which their organic or functional photophobia had previously cut them off, forcing them to strain for vision in a perpetual twilight.
In conclusion, it seems worth while to say a few words about the fluorescent lighting, now so extensively used in factories, shops and offices, on account of its cheapness. There is good evidence that this kind of lighting adversely affects the vision of a minority of those who have to do close work under it. One reason for this must be sought in the composition of the light itself, which does not come from an incandescent source, as does natural sunlight or the light from a filament bulb. Nor is this all. Fluorescent lighting throws almost no shadows. Consequently the element of contrast, so immensely important to normal seeing, is conspicuously absent from rooms illuminated by fluorescent tubes.
Shadows, moreover, help us in our estimation of distances, forms and textures. When shadows are absent, we are deprived of one of our most valuable guide-posts to reality, and the accurate interpretation of sensa becomes much harder. This is one of the reasons why the organs of vision tire so much more easily on a day of uniform high cloud than on one of bright sunshine. Fluorescent lighting produces an effect somewhat similar to that produced by the diffused glare reflected from high thin clouds. To eyes that have been evolved to adapt themselves to light proceeding from an incandescent source, and to minds that have learnt to make use of shadows as guides to correct interpretation, perception and judgment, fluorescent lighting cannot but seem strange and baffling. The wonder is that it is only a minority of people who react unfavourably to such lighting.
If you happen to belong to the unlucky ten or fifteen percent of the population which cannot work under fluorescent light without suffering from bloodshot eyes, swollen eyelids and lowered vision, the best thing you can do, of course, is to find a job which permits you to work out of doors, or by the light of incandescent filament lamps. The next best thing is to palm frequently, and get out of the fluorescence as often as possible for a few minutes of sunning. At night, as a substitute for sunning, take the light of a strong incandescent filament lamp upon the closed and open eyes. The movies constitute another excellent therapeutic measure for those who suffer in this way. Looked at in the proper way, they can be wonderfully restful and refreshing to eyes which react badly to the peculiar composition of fluorescent light and to minds which are baffled by the shadowless world of low contrasts, in which that light compels them to work.
APPENDIX I
After I had completed the manuscript of this book, a correspondent sent me a copy of the following article, contributed by a distinguished eye surgeon, Mr. Arnold Sorsby, to the pages of the British Medical Journal. This is what Mr. Sorsby writes.
Perfect Sight Without Glasses
A letter in this week’s Journal from Dr. J. Parness draws attention to a statement recently broadcast by Dr. Julian Huxley on the practice of correcting visual defects without the use of glasses. Before condemning such a practice it would be as well to examine the evidence in support of it. There are a variety of methods based on hypotheses of varying degrees of tenuity. The system expounded by W. H. Bates in his Cure of Imperfect Sight by Treatment Without Glasses (New York, 1920) has the advantage over competitive systems in that its principles are publicly stated. Bates holds that the refractive state is dynamic and is constantly changing. The changes in refraction are produced by the nerves and tissues of the extra-ocular muscles, the lens itself playing no part in accommodation.
Defective vision is a psychic phenomenon, affection of the brain centres first disturbing the macula and then the whole retina. Treatment aims at inducing “cerebral relaxation,” for when the mind is at rest vision is normal. In thirty years’ work on refraction Bates found few people who could maintain “perfect sight” for more than a few minutes at a time, and he often saw “the refraction change half a dozen times or more in a second, the
