JA 
NUARY, 1913 
HOUSE AND GARDEN 
27 
or 
four to five candle power per square inch, down to 0.2 to 
0.1 candle power per square inch as a minimum, are safe 
working standards for the eye. We are informed by the 
“Illuminating Engineer” that no absolute rule can be laid 
down, owing to “individually different requirements.” 
This is a bit nearer the mark, but there is one positive 
method of determining whether or not the source of light 
is too bright. If it can be regarded fixedly without ocular 
discomfort, squinting, or annoyance, it is not too bright 
from a physiological viewpoint. Whether it is a source 
of pleasure and a delight to the eye, is a psychological, 
esthetic problem, which we will discuss later. 
Do not confuse the “candle power” of “source brightness” 
“intrinsic b r i 1 - 
liancy” with the 
rated candle pow¬ 
er of the light it¬ 
self. The first is 
purely a measure 
of the brilliancy 
of various light 
sources expressed 
in candle power 
per square inch; 
and it is merely 
for comparative 
purposes that the 
reference is here¬ 
inafter used. 
Of course, in 
m a n y instances 
the eye is pro¬ 
tected from the 
dangerous bril¬ 
liancy of the 
tungsten lamp, by 
some sort of 
glassware, which 
should serve the 
double function 
of eye protection 
and the re-dis¬ 
tribution of light 
over areas where 
it is required. 
The fact remains, 
however, that no 
illuminant manufacturer has indicated the necessity for utilizing 
his product with care. Undue emphasis on its economical phase 
has persuaded the adoption of such lights in substitution for older 
types of less brilliant illuminants, but nothing has been said about 
eye strain and its prevention. 
Since the days of the candle the source brightness of our il- 
luminants has steadily increased. It has passed the danger mark, 
but the saturation point is not yet in sight. If values of from 
o. 1 to five candle power per square inch constitute the maximum 
range of brightness that is safe for human eye¬ 
sight, glance at the following tabulation, and 
cease to marvel at the oculist’s prosperity: 
From an inspection of the above it is apparent that each 
successive development of electrical illuminants has been 
attended with an amazing increase in source brightness, 
and where a value of five candle power per square inch is 
considered the limit of safety, we have exceeded that 
limit two hundred times! 
When this significant fact is realized the time will be 
at hand for serious consideration. 
The human eye is but an extended portion of the brain, 
according to the most eminent anatomists—and as such 
must be treated as no mere auxiliary optical equipment, 
but instead, as a vital anatomical organ affecting in some im¬ 
portant manner every other organ. Thus, the glaring unprotected 
light source, 
whether it be the 
typical light of 
the subway train 
or some too bril¬ 
liant light in the 
home, is the un¬ 
suspected cause 
of many an acute 
headache, which 
with continued 
exposure will be¬ 
come chronic. 
Indigestion a n d 
nervous despond¬ 
ency have also 
been traced to 
this cause. The 
physiological sig¬ 
nificance of color, 
or quality of light 
in the' h o m e, 
brings us to the 
reading page, 
great deal 
Whatever is good in decoration expresses a consistent relationship between light and color. I he 
atmosphere of the home as influenced by light should reflect refinement; do not desecrate its 
environment with commonplace lighting glassware typical of the store, the office and the factory 
Source of Light 
Jl' 
Candle . 
Oil lamp . 
Gas flame . 3 
Carbon filament electric lamp. 375 
Welsbach gas mantle. 20 
Tungsten lamp .1000. 
Intrinsic Brilliancy 
Candle Power 
Per Square Inch 
.... 3.-4. 
.... 3.- 8 . 
- 8 . 
■50. 
A 
of 
humanity’s ocular 
discomfort has 
come from en¬ 
deavoring to de¬ 
cipher small black 
characters against 
a white page. In 
the days of earlier 
illuminants the 
page was perhaps insufficiently lighted and eyesight was im¬ 
paired through strained perception. Then came the oil lamp 
with its soft mellow radiance, which has still many admirers in 
the student world. We see the small print on our reading page 
by contrast. The contrast is the black type against the white 
background, but the area occupied by the blank white paper is 
far greater than the area occupied by the black type. In other 
words, the blank, white area, which serves to reflect or dif¬ 
fuse light from a lamp into the eye, reflects more than is neces¬ 
sary to perceive the printed matter by contrast. 
With earlier forms of electric illuminants the 
white page was modified by the amber color of 
the light source, and against this soft, mellow 
background the contrast of the small black 
characters was less abrupt and more readily 
perceptible. With the tungsten lamp, the read¬ 
ing page is glaring white, reflecting so much 
light into the eye that comfortable perception 
is impossible. 
Assuredly we desire to enjoy the economic 
