142 
IOWA ACADEMY OF SCIENCE Vor. XXIX, 1922 
The two systems have been compared in many other particu- 
lars such as shadow production, pleasantness of illumination, color 
of lighting, cost of fixtures, uniformity of illumination, glare, 
and several others ; and comparison has also been made on the 
score of intensity required for the same kind of work. It is this 
problem which will be discussed in this paper. 
In 1907 2 Millar published some data, based on experiments 
with ten individuals, which showed that 2.7 foot-candles of direct 
lighting were required by these men to read newspaper print, and 
that 4.45 foot-candles were required to read the same print when 
the lighting was indirect. 
In 1913 3 T. E. Ritchie also published data on this point. He 
used seven persons and found that 7.3 foot-candles were required 
when direct lighting was used, and only 1.5 foot-candles when 
the lighting was indirect. In this case the print used for reading 
was that on the back of a slide rule. 
It will be seen that the two articles referred to yield contradict- 
ory conclusions. Again, many casual observers of lighting sys- 
tems give it as their opinion that less intensity is required from 
the one system, while others are convinced that less intensity is 
required by the other system. , 
These contradictions have opened anew the question of the 
relative intensities required under direct and under indirect light- 
ing systems, and it was also the hope of the writer to ascertain 
why a person needs more natural light for a certain kind of work 
than he does of artificial light. 
Accordingly, it was planned to make an experiment on a great 
number of individuals and under conditions such that the illu- 
mination would be decidedly diffuse in one case and exclusively 
direct in the other case. The room used for this experiment was 
30 feet long, 18^2 feet wide, and 13 feet high. The ceiling and 
upper half of the walls were painted white; the lower half of the 
wall and the floor were drab. 
For the direct lighting the lamps were hung seven feet above 
the floor, and opaque white enameled reflectors were used As 
this work was done at night (actually between 7 and 8 P. M.), 
the window shades were raised so that light was not reflected 
from them but passed out through the windows. Every precau- 
tion possible was taken to have the light on the book come only 
from the. fixtures direct. 
2 Trans. I. E. Vol. 2, p. 590 (1907). 
3 Ilium. -Eng., Vol. 6, p. 42 (1913). 
