Artificial Light | Page 5

few centuries ago upon certain prominent
points.

Signal-lights now guide the railroad train through the night. A burning
flare dropped from the rear of a train keeps the following train at a safe
distance. Huge search-lights penetrate the night air for many miles.
When these are equipped with shutters, a code may be flashed from one
ship to another or between the vessel and land. A code from a powerful
search-light has been read a hundred miles away because the flashes
were projected upon a layer of high clouds and were thus visible far
beyond the horizon.
Artificial light played its part in the recent war. Huge search-light
equipments were devised for portability. This mobile apparatus was
utilized against enemy aircraft and in various other ways. Small
hand-lamps are used to send out a pencil of light as directed by a pair of
sights and the code is flashed by means of a trigger. Raiding-parties are
no longer concealed by the curtain of darkness, for rockets and
star-shells are used to illuminate large areas. Flares sent upward to drift
slowly downward supported by parachutes saved and cost many lives
during the recent war. Rockets are used by ships in distress and also by
beleaguered troops.
Experiments are being prosecuted to ascertain the possibilities of
artificial light in the forcing of plant-growth, and even chickens are
made to work longer hours by its use.
Artificial light is now modified in color or spectral character to meet
many requirements. Daylight has been reproduced in spectral quality so
that certain processes requiring accurate discrimination of color are
now prosecuted twenty-four hours a day under artificial daylight.
Colored light is made of the correct quality which does not affect
photographic plates of various sensibilities. Monochromatic light is
utilized in photo-micrography for the best rendition of detail.
Light-waves have been utilized as standards of length because they are
invariable and fundamental. Numerous other interesting adaptations of
artificial light are in daily use.
This is in reality the age of artificial light, for mankind has not only
become independent of daylight in certain respects, but has improved
upon natural light. The controllability of artificial light makes it

superior to natural light in many ways. In fact, uses have been made of
artificial light which are impossible with natural light. Light-sources
may be made of a vast variety of shapes, and those may be transported
wherever desired. They may be equipped with reflectors and other
optical devices to direct or to diffuse the light as required.
Thus, artificial light to-day has numerous advantages over light which
has been furnished by the Creator. It is sometimes stated that it can
never compete with daylight in cheapness, inasmuch as the latter costs
nothing. But this is not true. Even in the residence, daylight costs
something, because windows are more expensive than plain walls. The
expense of washing windows is an appreciable percentage of the cost of
gas or electricity. And there is window-breakage to be considered.
In the more elaborate buildings of the congested portions of cities,
daylight is satisfactory a lesser number of hours than in the outlying
districts. In some stores, offices, and factories artificial light is used
throughout the day. Still, the daylighting-equipment is installed and
maintained. Furthermore, when it is considered that much expensive
area is given to light-courts and much valuable wall space to windows,
it is seen that the cost of daylight in congested cities is in reality
considerable. Of course, the daylighting-equipment has value in
ventilating, but ventilation may be taken care of in a very satisfactory
manner as a separate problem.
The cost of skylights in museums and other large buildings is far
greater than that of ordinary ceilings and walls, and the extra allowance
for heating is appreciable. The expense of maintenance of some
skylights is considerable. Thus it is seen that the cost and maintenance
of daylighting-equipment, the loss of valuable rental space and of wall
area, and the increased expense of heating are factors which challenge
the statement that daylight costs nothing. In fact, it is not surprising to
find that occasionally the elimination of daylighting--the reliance upon
artificial light alone--has been seriously contemplated. When the
possibilities of the latter are considered, it is reasonable to expect that it
will make greater and greater inroads and that many buildings of the
future will be equipped solely with artificial-lighting systems.

Naturally, with the tremendous development of artificial light during
the present age, a new profession has arisen. The lighting expert is
evolving to fill the needs. He is studying the problems of producing and
utilizing artificial illumination. He deals with the physics of
light-production. His studies of utilization carry him into the vast fields
of physiology and psychology. His is a profession which eventually
will lead into numerous highways and byways of