n the
nineteenth century, the aim was merely to reinforce daylight toward the
end of the day. Continuous operation of industrial plants was not
practised in those days, excepting in a very few cases where it was
essential. To-day some industries operate continuously, but most of them
do not. In the latter case the consumer pays more for the product
because the percentage of fixed or overhead charge is greater.
Investment in ground, buildings, and equipment exacts its toll
continuously and it is obvious that three successive shifts producing
three times as much as a single day shift, or as much as a trebled day
shift, will produce the less costly product. In the former case the
fixed charge is distributed over the production of continuous operation,
but in the latter case the production of a single day shift assumes the
entire burden. Of course, there are many factors which enter into such a
consideration and an important one is the desirability of working at
night. It is not the intention to touch upon the psychological and
sociological aspects but merely to look coldly upon the facts pertaining
to artificial light and production.

In the first place, it has been proved that in factories proper lighting
as obtained by artificial means is generally more satisfactory than the
natural lighting. Of course, a narrow building with windows on two sides
or a one-story building with a saw-tooth roof of best design may be
adequately illuminated by natural light, but these buildings are the
exception and they will grow rarer as industrial districts become more
congested. Artificial light may be controlled so that light of a
satisfactory quality is properly directed and diffused. Sufficient
intensities of illumination may be obtained and the failure of
artificial light is a remote possibility as compared with the daily
failure of natural light. With increasing cost of ground space,
factories are built of several stories and with less space given to
light courts, with the result that the ratio of window area to that of
the floor is reduced. These tendencies militate against satisfactory
daylighting. In the smoky congested industrial districts the period of
effective daylight is gradually diminishing and artificial lighting is
always essential at least as a reinforcement for daylight. It has been
proved that proper artificial lighting--and there is no excuse for
improper artificial lighting--is superior to most interior daylighting