DIRECT AND INDIRECT LIGHTING 
145 
between the two, the determination of which was the chief object 
of this experiment, is left practically unaltered. When we drop 
out the abnormal intensities we get an average of 2.77 foot-candles 
for the direct, and 4.13 foot-candles for the indirect It may be 
seen, therefore, that by the indirect system we need an intensity 
almost 50 per cent greater than that required by the direct system 
for the same kind of work. 
Since under the indirect lighting system everything in the field 
of vision is about equally illuminated, the pupil contracts much 
more than it does under the direct system, where much of the 
field is dark. 
In the latter case the pupil will enlarge to allow more light to 
enter and will soon come to a state where a person can read print 
comfortably even though the actual intensity is small. It seems 
then that the illumination intensity required depends quite largely 
upon the brightness of the objects in the field of vision. If they 
are as bright as the objects on which we wish to focus our atten- 
tion, then a high intensity is required ; if, on the other hand, they 
