CHAPTER VI
LIGHTING
Adaptability of Eye to Light
The eye has a great range of adaptability to the intensity of light. This is evidenced by the fact that the eye is readily adapted to the intensity of the bright sunlight or to the soft rays of the moon. In both instances there is no disturbance in vision, even though the intensity of illumination at midday when the light is brightest is almost a million times greater than the illumination from the full moon on a clear night. This adaptation takes place so perfectly and so independent of the educated mind that we give little thought to the great difference in intensity of light.
It must be remembered, however, that although this adaptation takes place so perfectly and without any apparent difficulty, it requires an expenditure of Innate force to accomplish this action. If the change takes place too rapidly from a soft light to an intense light, without sufficient time for adaptative action to take place, the delicate structure of the eye will be damaged by the violent light vibrations. The change from the soft rays of the moonlight to the intense illumination from the bright sun takes place gradually. First, the night; next, the gray dawn of morning; and then comes the sun, whose rays are softened as they pass through a maximum amount of atmosphere near the horizon, and as the sun approaches the dome of the arc, the rays become more intense, since they pass through less of the earth’s atmosphere. Then the process is reversed as the intense light from the sun gives way to the softer rays from the moon.
This gives Innate plenty of time to bring about the adaptative processes so necessary to adjust the eye to these extremes, time being a very important factor in all the processes of the body.
Thus it is appreciated that the subject of lighting is important from a hygienic standpoint, since improper lighting necessitates an unnecessary expenditure of energy and causes impaired health.
The Eye
That we may better appreciate this adaptability and have a clearer understanding of the mechanism through which Innate Intelligence accomplishes this adaptative action we will review briefly the organ through which we perceive light—the human eye.
The eye consists of a crystalline lens, powerfully refractive, held between two transparent liquids called the aqueous humor, which is in front of the crystalline lens and the vitreous humor, which is behind or posterior to the crystalline lens. The aqueous chamber is divided into an anterior and posterior chamber by the diaphragm called the iris, through which is an opening called the pupil, permitting communication between the chambers of the aqueous humor. The retina, which is composed of nervous tissue, lines the posterior five-sixths of the inner surface of the posterior wall of the eyeball. At the back of the retina and in the direct visual axis is a spot known as the macula lutea, a yellow spot, in the center of which is a depression known as the fovea centralis. At this point the vision is clearest and it is this spot used when we turn our eyes and look directly at an object.
With such a delicate instrument as the eye it is only reasonable that special care and arrangement should be supplied to protect it from sudden changes in the intensity of light. Otherwise the eye would be greatly injured by the glare of light. This adaptation is accomplished by means of regulating the amount of light admitted to the retina. This is done through the expression of Innate by regulating the size of the pupil.
When the eye is exposed to light, vibrations are carried to the brain through the afferent nerve fibers and Innate Intelligence becomes aware of the light. If it is intense and is allowed to remain in contact with the retina the delicate nerve tissue will be injured. To compensate for this Innate Intelligence sends motor impulses to the circular fibers in the iris, causing them to contract and decrease the size of the pupil and thus shut out a part of the light rays. In a less intense light or in the darkness the muscular fibers are relaxed, enlarging the pupil and admitting more light. In all of this adaptative action there must be sufficient time, although the action does take place almost instantly. This action is not automatic as some would have us believe, but is intelligent and under the direct control of Innate Intelligence.
If we were living in the natural state of man’s existence there would be no need for a consideration of these natural laws governing the working of the human body and the intelligence which controls these manifestations; but as man has increased his knowledge and has made for himself a more or less artificial environment, it becomes necessary for him to understand the natural laws that he may adapt his artificial environment to them. If man lived in the open outdoors there would be no need for the artificial lighting of buildings; but since he has created buildings it becomes necessary for him to study the laws of nature that he may produce a condition in this environment conducive to the expression of life. In providing artificial light for our buildings the laws of the physical organ of sight must be considered. However, the question of lighting is not alone one of artificial production of light in our buildings, but also deals with proper admission of natural light from natural sources.
Value of Sunlight
The value of the sunlight in respect to health has been recognized from time immemorial. Direct rays of the sun are essential in the development and expression of animal and plant life. The sun’s rays are Nature’s greatest germicide. They destroy almost all forms of germ life. Most of the chemical reactions are hastened or induced by the action of light. Light prevents or retards the development of the lower forms of life but promotes the growth of the higher forms.
Natural Light in Buildings
From the foregoing statement it is quite obvious that a proper amount of light, and if possible the direct rays of the sun, must be admitted to the home if it is to afford an environment at all conducive to the expression of life. It is therefore necessary to make special provision for the admission of light. The amount of light admitted to a building will be determined by its location and aspect, the source of the light, whether direct or reflected, the location and size of the openings, and the kind of glass used. The character of the walls and other inside surfaces will determine the light diffusion.
Since direct rays of the sun give more light than those reflected, it is desirable to admit them to the house as much as possible rather than to depend upon reflected light from the surfaces outside, such as the trees and buildings.
There is a certain loss of light as it passes through window glass. This loss is about 8% through plate glass while through double glass the loss is 10%, and through milk glass there is a loss of 50%. The amount of light in a room may be increased by the use of prism or ribbed glass which results in a more even distribution of light over the room.
The window area of rooms in a home should be not less than 10% of the floor area, or not less than one square foot of glass surface for every seventy cubic feet of interior to be lighted. This is not sufficient, however, for a schoolroom or for factories. The schoolroom should have a window area not less than one-fourth of the floor space.
Windows should be placed so as to admit direct rays of the sun and should extend within six inches of the ceiling. Window shades may be used to regulate the amount of light admitted, but care should be exercised in keeping down the dust, since it accumulates on the shades and is disturbed when they are adjusted. The dust then gets into the breathing zone and becomes objectionable from a hygienic standpoint.
Artificial Lighting
With the present day modern methods of artificial lighting it seems there would be little difficulty in lighting our homes and other buildings; but the question is not alone one of how they are to be lighted, but also how this can best be accomplished and not interfere with health and produce eye strain and other conditions that are likely to follow improper lighting.
It is interesting to note the evolution of the lighting systems from the primitive man who carried a burning stick from the campfire into his cave and thus realized the pleasure of the privacy of his own dwelling, up to the modern lighting systems. For centuries man burned wood and other materials in their natural state and depended upon these for his illumination. Then it was discovered that by dipping this raw material in animal fat more light could be obtained. Later the oil was placed in a container and a wick used. Then from this crude grease lamp with its wick evolved the candle, which was a great improvement over the former method. And so mankind groped in comparative darkness through centuries. It was not until the closing years of the nineteenth century that he found a better means of illumination. In 1879 Edison brought out his wonderful invention, the electric light. Even the evolution of this light would be interesting for there have been many improvements over the original.
It is very obvious that the best method of lighting is by the use of the incandescent electric light. It produces the desired intensity, does not vitiate the air, requires little attention, and is operated at a minimum expense.
The objections to the open blaze for illumination are that oxygen is consumed from the air, carbon dioxide and other impurities are given off, the light is not constant, since there is a tendency to flicker and especially so in a draft, it requires more attention, is unhandy to operate and does not give the proper amount of illumination. Most of these objections are overcome in the electric light.
The source of light must be so placed that it will not strike the eyes directly. Care must be taken that there are no surfaces reflecting light directly into the eyes. The lighting system must provide illumination of sufficient intensity, yet without a glare which produces eye strain. While our modern methods of artificially producing light are a great boon to civilization, they may also be a great detriment to health to say nothing of the discomfort that is caused by improper methods of lighting our homes, schools, and workshops.
Psychological Effect of Light
It is not out of order at this time to mention the effect of light upon emotions of the human family. Proper illumination is commensurate with the particular functions carried on within the place illuminated. Note the soft light effects of the cathedral and the influence it has on the people who visit the place. Enter a church building with its “dim religious light” and note the calming effect which it has on the assembly Of worshippers. To be sure they have gathered in the place for worship and are in that state of mind which would be expected of those in a revered mood, yet there is no question as to the influence of the surroundings and especially of the lighting. It would be quite out of keeping to have the cathedral as brilliantly lighted as the “Great White Way.” The architecture, the furnishings and the lighting all have a certain influence upon the minds of the individuals.
As the dim, soft light has a quieting influence so the bright, dazzling light has a stimulating effect. This is observed in the lighting of amusement places where the predominating feature of the entertainment is hilarity. The pulse may be made to beat faster, the thoughts turned from the serious things of life to the less serious, and the mind made to desire the activities of the pleasurable things of worldly enjoyment by the peculiar environment and the intensity of the illumination. Or the mind may be soothed into the tranquil moods and the entire being made to surge with emotion, while the mind is directed from the more frivolous subjects to the deepest thoughts of the philosopher with a proper arranging of the surroundings and a soothing and delicate lighting over all. While these things do not bear directly upon the subject of hygiene in the more commonly accepted way, yet they do have a certain bearing upon health and the physiological functions of the body, especially from the standpoint of environmental influence upon the body and its adaptation through the action of Innate Intelligence.
Systems of Lighting
Direct lighting is secured by fixtures which throw the light downward into the room from which the eyes are protected by properly adjusted shades. Indirect lighting is from bowl-like fixtures in which electric lights are placed and the light rays are reflected upward toward the ceiling with no light penetrating the bowl. Semi-indirect is accomplished by using a bowl which will permit some of the light rays to penetrate.
The best results are obtained by a combination of the direct and indirect methods of lighting and in some cases by a semi-indirect way. It has been observed that the direct rays of light should not fall squarely into the eyes. It is also quite essential that in some cases there should be direct rays on the work or object under observation. To accomplish this and at the same time to keep the light out of the eyes there must be a judicial use of shades and other means of softening the light.
There are some objections to the indirect method in that all the light is thrown on the ceiling. This gives a very soft light in the room, but is not sufficiently bright and faces lose their expression; there is insufficient modeling of objects, and the interior will be almost devoid of character. This form of lighting, therefore, is undesirable for home and offices, but is not objectionable for places of amusement.
There are also objections to the direct system since the strong direct light makes too harsh shadows and a light glare which is very objectionable. By properly diffusing this direct light and adding sufficient upward light we get a much more effective and pleasing illumination.
By using the two systems, or better still, by combining the two systems into the semi-indirect, a method is obtained which will furnish an abundance of light and at the same time give one that is so perfectly diffused there will be no objectionable shadows and no harmful glare.
Insufficient light may be quite as injurious to the eyes as too much light. As a matter of fact it is not so much a question of too great an intensity as it is of the proper light direction; it is hardly possible to get a light of greater intensity than that of the sun, but we are very careful that the sun’s direct rays do not enter the unprotected eye; neither is it good to permit the reflection of the rays into the eyes, as from a printed page.
(For schoolroom lighting see chapter on School Hygiene.)