tigation showed that this value
varies usually between 30 to 70 cents per square foot per year. Using
the mean value, 50 cents, it is seen that the rental charge is about
seven times the cost of lighting. Furthermore, there is a saving of 43
cents per square foot per year during the night operation by operating
the night shift. Of course, this is not strictly true because a
depreciation of machinery during the night shift should be allowed for.
These fixed charges would average slightly more than half as much in the
case of the two-shift factory as in the case of the same output from a
factory twice as large but operating only a day shift. Incidentally, the
two-shift factory need not be a hardship for the workers, for, if the
eight-hour shifts are properly arranged, the worker on the night shift
may be in bed by midnight and the objection to a disturbance of ordinary
hours of sleep is virtually eliminated.

In a discussion of light and safety presented in another chapter the
startling industrial losses due to accidents are shown to be due
partially to inadequate or improper lighting. About one fourth of the
total number of accidents may be charged to defective lighting. The
consumer bears the burden of the support of an unproducing army of idle
men. According to some experts an average of about 150,000 men are
continuously idle in this country owing to inadequate and improper
lighting.

This is an appreciable factor in the cost of living, but the greatest
effectiveness of artificial lighting in curtailing costs is to be found
in reducing the fixed charges borne by the product through the operation
of two shifts and by directly increasing production owing to improved
lighting. The standard of artificial-lighting intensity possessed by the
average person at the present time is an inheritance from the past. In
those days when artificial light was much more costly than at present
the tendency naturally was to use just as little light as necessary.
That attitude could not have been severely criticized in those early
days of artificial lighting, but it is inexcusable to-day. Eyesight and
greater safety from accidents are in themselves valuable enough to
warrant adequate lighting, but besides these there is the appeal of
increased production.

Outdoors on a clear summer day at noon the intensity of daylight
illumination at the earth's surface is about 10,000 foot-candles; in
other words, it is equal to the illumination on a