Light, its use and misuse : a primer of illumination

355

GIFT

LIGHT

ITSUSE-'MISUSE

OF THE

LIGHT:
ITS USE AND MISUSE

A PRIMER OF ILLUMINATION PREPARED
UNDER THE DIRECTION OF THE
ILLUMINATING ENGINEER-
ING SOCIETY

A*

COPYRIGHT 1912 BY

ILLUMINATING ENGINEERING SOCIETY

29 WEST 39th STREET, NEW YORK

x

ILLUMINATING
ENGINEERING SOCIETY

THE ILLUMINATING ENGINEERING
SOCIETY was organized in 1906 to ad-
vance the theory and practise of illuminating
engineering and to disseminate knowledge
relating thereto. The Society now has about
1600 members who are interested in the sub-
ject of lighting from various standpoints :
engineering, economic, hygienic, esthetic.

The Society has no affiliation with any com-
mercial organization. Any one interested in
its objects may become a member.

LIGHT: ITS USE AND MISUSE1

It is the purpose of this publication to assist the user in mak-
ing artificial light effective, whether the light be produced by
oil, gas, electricity or otherwise.

By proper use you can get good illumination from any of
these sources, but by misuse you are likely to get lighting that
is bad, costly, and even dangerous to the eyesight.

ILLUMINATION AND COMFORTABLE VISION

To see easily and comfortably you must select the lamps,

Fig. 1. — The eye: essential parts shown in section.

fixtures and globes and arrange the lights so as to best suit the
particular conditions which have to be met, but certain prin-
ciples which must always be followed may safely be laid down.2

Fig. 2.— Pupil of eye ex-
panded to let in plenty of light
when illumination is dim.

Same pupil contracted to shut
out excessive light.

1 A primer of illumination prepared under the direction of the Illumi-
nating Engineering Society. (Copyright 1912.) Applications for per-
mission to reprint this primer should be addressed to the Illuminating
Engineering Society, 29 W. 39th Street, New York.

2 To understand these principles better, take a glance at the eye and

254064

2 LIGHT : ITS USE AND MISUSE

Don't Judge Illumination by the Brightness of the Lamps

Judge the light you are getting by the way it helps you to
see. Do not think because a lamp looks glaring and brilliant
that it is giving you good light. It may be merely giving you
too much light in the wrong place. On the other hand, a
well shaded table lamp may look dim because it is well shaded,
and still be giving first-class light for working purposes.

You must get enough light to see by, and as you see things
chiefly by the light which they reflect, it is evident that dark
colored objects which reflect light badly require more light than
do light colored objects to see them comfortably. That which
is quite sufficient for sewing on white cloth, for example, will
not do at all for working on black cloth.

Don't Work in a Flickering Light

See that your light is steady. If you leave a dark room and
go into bright sunshine the sensation is unpleasant to the eye ;
if you use a light that flickers, you get this same unpleasant
sensation, perhaps as rapidly as twenty times a minute. Fur-
thermore, the eye endeavors to adjust itself to suit the light ;
if the light flickers it keeps the iris of the eye "see-sawing,"
as it were, and the muscle that governs it gets tired and reacts

see how it works. Figure 1 shows the parts of the eye as they would ap-
pear if it were cut through from back to front vertically.

In the process of seeing, the light passes through the cornea, pupil, and
lens of the eye to the retina, just as in a camera light passes through the
lens to the sensitized film. The picture is formed on the retina, which is
a layer made up of the ends of nerve fibers which gather into the optic
nerve and go directly to the brain. The optic nerve sends along the pic-
ture to the brain for notice. The lens of the eye, unlike that of the camera,
automatically changes in thickness to focus or make a clear image on the
retina for seeing at different distances. This focusing action is called the
accommodation of the eye, and when the light is dim or bad the focusing
muscle vainly hunts for some focus which may make objects look clear and
gets tired in trying to do it. The muscles which move the eye about also
get tired in the same way and the result is eye-strain, which stirs up pain
and headache just as any other over-tired muscles of the body may set
up an ache.

The iris (which gives the eye its color) serves to regulate the amount
of light which reaches the eye. In very dim light it opens out making the
pupil big, as shown in figure 2, and in very bright light it shuts up as
shown, and thus keeps out a flood of brilliant light which might hurt the
retina. The protective action of the pupil is pretty good, but by no means
complete, for it seldom gets smaller than shown in the illustration, how-
ever bright the light.

LIGHT: ITS USE AND MISUSE 3

on the nerves to cause discomfort and pain. Reading in railway
trains causes similar strain ; the eye muscles get tired in trying
to follow the shaking page, and are likely to provoke a headache.

Don't Expose the Eyes to an Unshaded Light
It is bad to have an unshaded brilliant light glaring into the
eyes, for it throws hard labor upon them in an effort at adjust-
ment. This applies even to common electric, gas, or oil lamps.
(See figs. 3, 4, 5.) While artificial light may be made a good

Fig. 3.— Very bad lighting. This man receives, full in the face, both

direct light from the unshaded lamp and reflected

glare from the table top and papers.

substitute for daylight, you have constantly to beware lest rays
that are too bright, either from the lamps or from their reflec-
tions, hurt the eyes. You can get reflections, so bright as to
be harmful, from polished metal or glass, from bright varnished
surfaces, or even from glossy white paper upon which the
light falls.

A bright light fairly in the field of view means a very brilliant
light on the retina, producing fatigue. Everyone knows the
blinding sensation of looking at the sun with its sequence of

LIGHT: ITS USE AND MISUSE

dazzling colored images. Babies are here common sufferers
when careless mothers or nurses allow them to lie in their car-
riages with eyes exposed to the unclouded sun. Bright arti-
ficial lights, in a less degree, do the same thing to all of us.
And when you get a bright light in the field of view, the pupil
tries to shut it out ; in so doing it renders less bright things

Fig. 4. — Faulty arrangement of dining-room lighting. The lamps exposed

in the dome shine in the eyes. Trouble is aggravated by

general darkness of the room.

all but invisible. Thus it is hard to see things which are
nearly in line with a brilliant light, as you often find in facing an
automobile headlight, or looking into a show window like fig. 6.

Place an unshaded lamp in front of a picture
A Couple of on the wall and then gtand back a f ew f eet and

Simple Experiments

note how much of the picture you can see

clearly. Then hold a book or paper at arm's length so as just
to cover the bright light and note the way in which the pic-

LIGHT: ITS USE AND MISUSE 5

ture clears up. Again, put an unshaded lamp about a foot in
front of your eyes and try to read a newspaper just beyond it.
Then shade your eyes from the lamp and try it again. You
will soon find out in this way that lamps can be so placed that
they will be a hindrance rather than a help in seeing. (Com-
pare fig. 7 with fig. 6.)

Prom time immemorial mankind has received
its light mostly from the sky. Consequently
the part of the retina on which the light from
above chiefly falls is pretty well used to it, while bright light

Best Direction
of Light

Fig. 5.— These ladies are annoyed by the glare of the unshaded light when

they look across the room. Common and faulty arrangement.

Lamps should be enclosed in diffusing globes.

from below, falling on the part of the retina which commonly
gets light only from grass or dark pavements; may be very ir-
ritating and unpleasant. Thus the glare from snow and sand
is not only disagreeable on account of its intensity but because
of the unusual direction from which it comes. Just so with a
brilliant beam reflected from glossy paper on which you are
writing. Its rays strike you from an unusual direction and
are harmful for that reason. Other smooth and shiny sur-

LIGHT: ITS USE AND MISUSE

Fig. 6. — Poor arrangement for display. You see the lamps
instead of the sweets.

Fig. 7. — Excellent arrangement for display. No lamps in sight.
Every garment is brightly lighted.

LIGHT: ITS USE AND MISUSE 7

faces deliver an equally hurtful assault on that sensitive and
much abused organ,— the eye.

Don't Read Facing the Light

It is best to have the light come from above and somewhat
sidewise, as it commonly does in nature, so that you will not
get a brilliant reflection or glare from what you are trying to
see. In reading and writing it is better to have the light come
from the left, to avoid getting a shadow of the hand that holds
the book or pen. Let the lamp be just far enough behind to
keep direct reflections from the paper out of the eyes. (See
figs. 8, 9, 14, 15.) But what has been said of reflections from
paper applies with even more force to the case of polished metals,
or the like, over which one is busy. Individual lights placed close
over the work are very likely to produce these troublesome
direct reflections and consequently such lights are falling into
disuse. In an interior otherwise dark, their use is open to the
further objection of giving bright spots of light and so pro-
ducing too violent contrasts of light and shade. (See figs. 16, 17.)

Don't Use a Bright Light Against a Dark Background
Almost any light will glare unpleasantly if the surroundings
are thoroughly dark. As an extreme illustration, the light
from a big arc lamp hung close to the sidewalk may be very
annoying at night, but by day you would hardly notice it. Just
so a bright lamp against a dark background may be annoying,
while against a light background it would not be so unpleasant.

LAMPS, FIXTURES, GLOBES, REFLECTORS

One may choose to-day among lights of many kinds. There
are at hand candles, oil lamps, open flame gas jets, upright and
inverted mantle gas lamps, electric incandescent lamps of car-
bon and of tungsten, electric arcs of half a dozen varieties,
besides mercury- vapor tubes, acetylene lamps, as used on mo-
tor-cars, and so on through a long list.

What do you wish to use a light for ? To read or write by,
to bring into view the working parts of a machine, to match
colors, to display goods, or pictures ; or merely to make a path-
way safe and plain ? Each case is to be studied by itself, and
the effect is to be accomplished by such lamps, globes and re-
flectors as, properly disposed, will insure ample lighting with-
out glare, and yet with strict economy.

8

LIGHT: ITS USE AND MISUSE

However good and suitable the lamp, it will be put at a dis-
advantage unless the lighting fixture which carries it is
designed to hold the lamp in the right position to enable one
to best utilize the light which comes from it. Prettiness in a
fixture is well enough ; but let the fixture be serviceable first ;
then it may be also as pretty as you please. But don't buy
prettiness if it makes war on good service.

Daylight is naturally well diffused ; but artificial light, poured

Fig. 8.— A bad position for reading. In spite of the shaded lamp, glare
from paper reflected into eyes, is very trying and harmful.

out as it is from mere points, or narrow surfaces, needs to be
tempered or softened by shades. And it sometimes further
requires to be directed upon a desk or table or other object.
In some cases it is better to adopt indirect methods, and throw
the beams of a lamp upon a ceiling whence the rays are scat-
tered. For every particular need there is ample provision
amid the abounding lamps, globes and reflectors of present
day designers.

Arranging Lights

LIGHT: ITS USE AND MISUSE 9

Two methods are usual in arranging lamps :
first, to secure general illumination by so plac-
ing the lamps that you may see with comfort anywhere in a
room ; second, in cases where a bright light is not necessary
throughout a room, local illumination can be planned, placing
the lights where they will be most used, always remembering

Fig. 9. — Good position in reading. No light directly hits the eyes
and no glare is reflected from the book.

that it will not do to localize light too much, since you need
for comfortable seeing a fair quantity of light broadly dis-
tributed.

PRECAUTIONS TO BE TAKEN IN PLACING
AND SHADING LIGHTS

In any artificial lighting the lamps should be so well shaded
that the eye does not see them directly nor brilliant reflections

io LIGHT: ITS USE AND MISUSE

from them. You can accomplish this end by putting the light
Diffusing and in diffusing globes of, for instance, ground glass

Shading by Globes or white or opal glass or other translucent ma-
and Reflectors terial. To secure the best diffusion, the globes

should be dense enough not to reveal the form of the actual
light source within, but to give the effect of the light pouring
forth from the globe as a whole. (See fig. 10.)

Another way of accomplishing the same result is to put a
shade around the lamp, which screens it and reflects downward
much of the light which would otherwise idly fall on the walls
or ceiling. (See fig. 11.) Such shades may be of mirrors or

Opal glass globe. Ground glass globe.

Fig. 10. — Within each globe is a lamp of the same candle-power.
Note the superior diffusion of the light by the opal globe.

polished metal or white or opal glass, of ground or prismatic
glass,— all of which, in a measure, work alike. Glass shades
are generally preferable to metal ones, for a little light pene-
trates them sidewise,— just enough to keep the upper part of
the room from being too dark.

Another scheme successfully used to shield the
light is to turn the light from the lamp upward
on to the ceiling by means of an opaque reflector underneath.
The reflector conceals the lamp, and the brightly illuminated
ceiling by which the light is diffused serves as the actual
source of the illumination. (See fig. 12.) This plan should
be used only on white or very light ceilings and is subject to a
heavier loss for securing diffusion than some other methods,

LIGHT: ITS USE AND MISUSE u

but often this loss is reimbursed by the thoroughness with
which the ceiling diffuses the rays that fall upon it.

Don't Use Local Lighting by Itself

In ordinary cases general illumination is the best way of
lighting an interior unless some of the work in

General Illumination han(^ ag sewing dark goods or reading very fine

print, demands exceptionally strong lighting in

Fig. 11.— General illumination by direct lighting; lamps concealed

in diffusing glass reflectors.

.

some parts of the room. In this case local lights may be added,
but they .ought not to be used without pretty strong general
illumination. The commonest sort of localized lighting is that
furnished by a table lamp. Such a lamp should always be
shaded to keep the direct light out of the eyes,— best by a
translucent shade which will add something to the general
illumination.

In any one of these plans for general illumination, lights
should be so placed as to give at least fairly uniform lighting

12

LIGHT: ITS USE AND MISUSE

everywhere in a room, otherwise there may be strong and jar-
ring contrasts of light and darkness.

In using shades open at the bottom, such as are very com-
mon, their shape and character can be so chosen as to distribute
the light precisely as desired ; this result can in less degree
be accomplished by using enclosed globes or by indirect lighting.

Fig. 12.— General illumination by indirect lighting; lamps are concealed
in opaque reflectors and the light is diffused from the ceiling.

Any of the schemes here sketched can be made to give good
results. The choice between them turns upon just what task
is required of the light and what its surroundings are to be.
Ordinarily, lighting from shades open at the bottom gives a
stronger light than other methods, but you must carefully
avoid glare in these cases. Lighting by wholly indirect means,
in which all the rays are diffused from the ceiling, demands
lamps of extra power for the same illumination, but requires
little care to avoid glare. Rooms lighted from diffusing globes
take an intermediate position with respect to freedom from glare.

LIGHT: ITS USE AND MISUSE

(a) Concentrating re-
flector : lights a small
area brilliantly.

/b) Semi-concentrat-
ing reflector: lights a
larger area less bril-
liantly.

(c) Distributing re-
flector: lights a wide area
moderately.

— — — — — •-- -• — ^—•^—^•^•1

Fig. 13.— Reflectors put the light where you want it; (a), (b), and (c)
have lamps of the same candle-power. (These pictures are in-
tended only to show, in a general way, the effect of different types
of reflectors.)

14 LIGHT: ITS USE AND MISUSE

For a lamp to do its best work, it should not be

Misplaced Brackets . „ .„ ;, .

too near a wall, especially if this wall is dark.
Hence only very small rooms can be well lighted by the usual
side brackets, say 4 to 6 feet high. In a large room the eye
cannot avoid glare from such brackets unless their lamps are
so heavily shaded as to dim the room. In large rooms where
brackets can be placed high enough to be out of the general

Fig. 14. — Don't place a desk lamp like this; it glares from the
paper and shines in your eyes besides.

view, they may be used to advantage ; and they are often
convenient for occasional use, as in bedrooms, when the room
is also lighted by other means.

ECONOMY AND EFFICIENCY
Don't Waste Light by Using the Wrong Reflectors
By using reflectors you can put the light from a lamp where
it will do the most good, much as an automobile headlight

LIGHT: ITS USE AND MISUSE 15

sends the light along the road just where it is wanted. In
fig. 3 there is a lamp without any shade or reflector and
you will see that the light goes in all directions, only a
small part of it falling on the level of the table where it is
needed. The rest hits the walls and is reflected about the
room losing intensity at each reflection. Obviously an un-
shaded lamp does not throw the light where it is wanted. To
ensure the light falling upon the table you must use a reflec-
tor that will bring it there.

Fig. 15. — If you must use a desk lamp, put it in this position. If an open

reflector is used let it be of the diffusing type. Better still is a

reflector with a diffusing glass bottom.

Of such reflectors there are three general types, either of
glass or of metal, which we may call concentrating, semi-con-
centrating, and distributing. (See fig. 13, (a), (b) and (c).)
The first acts almost like an automobile headlight, throwing
its light downward into a comparatively small area. The sec-
ond kind spreads out the light over a much wider area, of
diameter perhaps as great as the height of the lamp above the

i6

LIGHT: ITS USE AND MISUSE

table, while the third is planned to light a comparatively big
area not very intensely at any one spot.

No reflector ever increases the total light that streams out
of a lamp ; it only puts the light where it is needed instead of
letting it go unguided.

Fig. 16.— More light in the eyes than on the work and
not enough light in the room. Sharp shadows and
much glare from the polished metal. Discomfort
to the worker: loss to his employer.

Don't Use Shallow Reflectors

All reflectors should come far enough down over their lamps
to prevent you from seeing the bright sources of light them-
selves without actually looking upward.

Hekht of Lam * With proper reflectors, their height above the
table, counter, or bench ordinarily makes little

LIGHT: ITS USE AND MISUSE 17

difference since it is the purpose of the reflectors to send the
light where it will do the most good.

Because dark walls absorb light strongly in-
stead of reflecting it they demand much
stronger lamps for sufficient illumination than
do light walls. (See fig. 18.) A very dark wall-paper or a
dark wood finish may require three or four times as much
light as a really light finish. Dark reds, greens, and browns
reflect pnly 10 to 15 per cent, of the light which falls on them.

Effect of Dark Walls
and Colored Globes

Fig. 17.— Example of good general illumination in a factory; the whole
area is uniformly and brightly lighted.

White, cream color, and light yellowish tints may reflect over
one-half the light.

Likewise, deeply tinted globes and shades absorb much light,—
a fact which must be borne in mind in considering economy.

Don't Let Lamps and Globes Get Dirty
Dirt on lamp chimneys, electric bulbs, globes, or reflectors
absorbs and wastes much light. The country over, it is safe to

1 8 LIGHT: ITS USE AND MISUSE

say that millions of dollars are wasted every year by letting
lamps become foul and dust laden. Nor is there any economy
in using electric bulbs until they blacken. It pays to renew
promptly blackened bulbs and defective gas mantles.

Don't Save Light at the Expense of Your Eyes

Saving light at the cost of eyesight is false economy. To

Real and False get good lighting it is generally necessary to

Economy diffuse the light from the lamps either directly,

by opal or ground glass shades, or indirectly, by turning the light

Fig. 18. — Each of these two little rooms receives the same

light. Dark walls absorb most of the rays of

light in left-hand room.

first on the ceiling or wall. The use of ground glass involves the
absorption of 15 to 20 per cent, of the light to secure diffusion,
opal glass of various kinds from 20 to 40 per cent., while some
forms of art glass and most diffusing ceilings absorb more than
half the light that falls upon them. Even though all these ap-
pliances absorb light in the process of diffusion, there is gain in
their use because they yield rays more grateful to the eyes.
But your eyes may tire easily even with good lighting. If so,

LIGHT: ITS USE AND MISUSE *9

consult an oculist and don glasses if you need them. Eye-strain
often comes from defective eyes as well as from faulty lights.

In gas lighting there is no economy in using
Economy in .

Selecting Lamps open name burners unless the exposure is such

that gas mantles would often be broken. Sim-
ilarly, with electric lights it is very wasteful in most cases to
use carbon filament lamps when tungsten lamps are available.
The carbon lamps cost less to install or replace, but much

more for electric current.1

•

AMOUNT OF ILLUMINATION REQUIRED

The common unit of illumination is the foot-candle, mean-
ing thereby the light which the object would receive from a
standard candle at the distance of one foot. This is the meas-
uring rod, as it were, by which comparisons are made.

No absolute rule can be laid down for the number of foot-
candles required for good seeing. Individuals differ widely in
their requirements; and the conditions under which the light
is used cause still greater variations in requirement. How-
ever, where lighting arrangements are well planned it has been
found by experience that ordinary reading, writing, or work on
white or light colored material, can comfortably be carried on
by most people with an illumination of 2 to 3 foot-candles. For
sewing dark goods, or reading fine type, 5 foot-candles are none
too much, while for drafting, engraving, watchmaking, work-
ing on black cloth, and the like, from 7 to 10 foot-candles should
be furnished.

1 The amount of electricity taken by an electric lamp is expressed in
watts. Most electric lamps now manufactured have the
number of watts which they are rated to consume
printed on a label on the bulb. The old-fashioned car-
bon filament incandescent lamp of 16 candle-power has the candle-power
on the label, and takes from 50 to 60 watts.

To determine the cost of operating an electric lamp, divide the number
of watts it consumes by 1000 to reduce to kilowatts, and multiply the
number of hours the lamp is to be operated by the kilowatts to obtain
the kilowatt-hours of electrical energy. The kilowatt-hours multiplied by
the rate per kilowatt-hour which is charged gives the cost of operation
for the stated time.

The consumption of gas lamps is expressed in cubic feet of gas per hour.
The number of cubic feet of gas per hour taken by a burner, divided by
1000, and multiplied by the cost per thousand cubic feet of gas, and by
the hours of burning, gives its cost of operation for the stated time.

The consumption of open flame burners is commonly taken at 5 cubic
feet per hour. Upright single mantle burners usually take from 3^ to 5
cubic feet per hour, though some smaller ones take less. Most individual
inverted gas mantle burners take from 3 to 3^ cubic feet per hour.

26

' LIGHTS 'ITS USE AND MISUSE

Artistic Effects

In a room suitably arranged for comfortable
seeing, you may have plenty of light, but the
general effect may be displeasing. The illumination may quite
fail to bring out the good points of the room in architecture
and decoration, or may play pranks with the appearance of
persons or things in the room. (See fig. 19.) One may not
object to ghastly tints in a factory, but in lighting a drawing
room such effects would not be tolerated. Hence one often

Bust lighted from above and in
front.

The same bust lighted from di-
rectly overhead.

Fig. 19.— Bad lighting defeats good art.

should sacrifice strict economy to get the most pleasing effect
in the room. The fixtures that carry the lights should har-
monize with their surroundings if the general effect is to be
agreeable. Handsome fixtures have a decided decorative value
whether their lamps are lighted or not. As strongly colored
objects give something of their own hue to all the light which
they reflect, the color of lamp shades, walls, and furnishings
plays an important part in the artistic effect.

i Z T*±± XT' I TOT? H

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