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other art directors as a system which might be used
with interesting results, for I personally have not
developed it beyond the experimental stage. Its
efiects are probably due to the fact that liehl vibrations
of difierent colors do not focus on th. ,u-.
plane in the retina of the eye, and as one recedes
and another advances we get an effect of depth.
When we come to paint a difficult set, we suddenly
get very friendly with the cameraman. We
realize he probably knows better than we do how
a color will photograph, but does he know ',Why?,,
It is that "*hy" we want to arrive at, so the object
of my talk tonight is to lead up to that question.
Mn. Vorcx: We are honored to have with us
tonight a famous research engineer, a man of international
fame, Mr. Loyd A. Jones, of the Kodak
Research Laboratories, Rochester. N. Y.. who rvill
read a paper on "Color Values Under Incandescent
Tungsten Illumination."
MR. JONES' PAPER
ON COLOR VALUES
In the analysis of the effects produced by the action
of certain definite causesr we may be content
in some cases to describe the observed reiults in qualitative
terms. Thus, in dealing with the question o{
the photographic rendition of color under any specified
conditions of illumination and photographic
material characteristics, we mav sav that a red
object is rendered as a lighter ton. Lf gray when
photographed (on Panchromatic film) tnder Incandescent
Tungsten illumination than when photographed
by the light from a sun arc. Such a statement
is, however, far from satisfactorv to the critical
student of such problems who undbubtedly will
ask immediately, what particular red are you talking
about and how much Tighter is it rendered under
tungsten illumination. He desires and needs
not only qualitative information. but also quantitative
information, so that he may know definitely the
effect produced by the use of tungsten illumination.
Nor is he yet satisfied; for if he is to fullv understand
the photographic tonal rendition of colored
objects, to be able to apply his knowledge to practical
problems, and to predict with certainty the
tonal rendition of any color under any illumination
of specified quality, he will surely want to know
why rcd is rendered as a lighter tone of gray when
tungsten lamps are used for illuminatine the red
object. Thus, to fully satisfy the requiriments of
complete understanding, we must be prepared to
lupply not only qualitative (how?) in{ormation,
but also quantitative (how much?) data; and further
to explain zthy the observed results occur.
Perhaps some individuals, of the so-called practical
school, may feel that they are not particularly
concerned with those theoretical aspects which are
involved in explaining why certain effects are produced,
but may be quite satisfied with a knowledee
of zuhat happens. However, I believe firmlv in the
premise that the nearest approach to perfection in
the practice of a scieirce can be attained with sreater
facility and certainty through an adequate knowledge
of the theoretical aspects of the subiect. The
earlier parts o{ this paper, therefore, will be devoted
to a discussion of certain essential physical
and psychophysical laws and relationships which
must be understood in order to explain why colors
are rendered as they are under tungsten and other
illuminants.
The fundamental knowledge essential to a complete
understanding of the photographic rendition
of colored objects may, for convenience, be classified
as follows: (a) The quality or spectr:al comfosition
of the radiation emitted by the various light
sources in which we are interested. (b) The characteristics
of the human eye as a sense organ responding
to stimulation by radiant energy o{ various
wave-lengths. (c) The characteristics of the objects
which it is desired to photograph, particularly their
capacity to reflect or transmit radiant energy of
various wave-lengths. (d) The characteristics of
photographic materials as light sensitive receptors
responding to rad,iant energy of various wavelengths.
We shall now proceed to a detailed consideration
of each of these subdivisions in the order
mentioned.
When radiant energy of certain definite wavelengths
falls upon the retina of the eye, a sensation
is produced which we call light. Thus, radiant energy,
a purely physical or objective phenomenon,
when allowed to act upon one of our sense organs,
the retina, serves as a stimulus producing a subjective
sensation or response which in general is designated
as light. Likewise, when radiant energv oi
certain wave-lengths, which may or may not be the
same as those producing the sensation of light, falls
upon a photographic plate or film, a resfonse (latent
image) occurs which by development can be rendered
visible and used as a means of producing a
pictorial representation of the objects from which
this radiation emanated. In order to analyze precisely
the correctness of tonal rendition obtained by
using any particular illuminant or source o{ radiation
for the reproduction of a series o{ colored objects
by the photographic process, it obviously is
necessary to have quantitative knowledge relative
to the characteristics of the radiation in question as
well as to understand the nature of both the visual
and photographic responses to this radiation.
It is assumed, in this discussion of the rendition
of color values under tungsten illumination, that
we are concerned only in the use of panchromatic
photographic materials, and moreover, that we are
interested in the rendering of colors when tungsten
illumination is used as compared with the rendition
obtained by.the use o{ other available illuminants.
Since the quality of the radiation emitted by an illuminant
has a profound inlluence upon the photographic
rendition of colors, it will be necessary, first
o{ all, to consider the way in which the quality o{
tungsten rad.iation differs from, or is similar to that
of the radiation emitted by other commonly used
light sources.
The quality, or spectral composition of radiation,
f ta1
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