VISUAL ACUITY WITH LIGHTS OF DIFFERENT
COLORS AND INTENSITIES

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INTRODUCTION

Although the problems of vision in general, and in particular
those of the comparative luminous and physiological effects of the
different colors of the visible spectrum, have for many years claimed
a large share of the time and thought of investigators in the fields
of physics, physiology and psychology, attention has been centered
largely upon theoretical considerations. Little effort has been made
to give practical application to the principles of color vision which
have been established as a result of these investigations, except in
so far as they have had reference to esthetics and pictorial art. The
artist knows very definitely what combinations of colors should be
made in order to produce the effects he desires, but on the other hand
the average person of intelligence knows only in the most general
way, if at all, what intensities of illumination or what colors of light
are best adapted to the purposes of ordinary vision.

This general indifference to the subject of the luminous efficiency
of different sources of light has been due largely to the fact that
until comparatively recent years the range of intensities and colors
available for purposes of artificial illumination has been very much
restricted. With the exception of the oxy-hydrogen flame, which is
too inconvenient and cumbersome for use outside of the laboratory,
the only artificial sources of light available were the incandescent
vapors of oils and the ordinary illuminating gas. As both these
lights are of approximately similar hue, the question of color differ¬
ences was never raised, and inasmuch as the intrinsic brightness
of each is very low, the only problem involved in their use was that
of getting sufficient light from them. Excessive cost and physical
limitations precluded the danger of injuriously high intensities of
illumination under ordinary conditions.

The last twenty years, however, have brought about a complete
revolution in the field of artificial illumination. The utilization of
electrical energy for lighting purposes in the various forms in which
it is now employed, and the remarkable development of the incandes-

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