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.)