Harry J. Keegan

Spectral properties of plants

The spectral properties of plant leaves and stems have been obtained for ultraviolet, visible, and infrared frequencies. The spectral reflectance, transmittance, and absorptance for certain plants is given. The mechanism by which radiant energy interacts with a leaf is discussed, including the presence of plant pigments. Examples are given concerning the amount of absorbed solar radiation for clear sky and overcast conditions. The spectral properties of desert plants are compared with those of more mesic plants. The evolution of the spectral properties of plant leaves during the early growing season is given as well as the colorimetric behavior during the autumn.

Spectrophotometric and Colorimetric Determination of the Colors of the TCCA Standard Color Cards

The color cards of the Textile Color Card Association of the United States are widely used in the textile and allied industries and by many procuring agencies of the federal government. The Textile Color Card Association issues both seasonal and standard color cards. The seasonal cards provide a color forecasting service to textile manufacturers and promote color coordination among the trades; the standard cards present colors for which there is a popular and continuing demand. Most important of the color cards is the Standard Color Card of America, the current ninth edition containing 216 colors. Pre-eminent among the many special sets of color cards issued by the Association for use of the federal government is the United States Army Color Card showing 22 official colors for the arms and services. The specification of the colors of the Ninth Edition Standard Color Card and the United States Army Color Card has been undertaken for the purpose of correlating these textile standards with American War Standard Z44—1942 for the specification and description of color. The 238 samples comprising these color cards have been examined by basic spectrophotometric and colorimetric procedures. From this study there have been found daylight reflectance, Y, chromaticity coordinates (x, y), Munsell renotations, and ISCC-NBS color designations for these samples as recommended by American War Standard Z44—1942. Since more than half of these textile standards are fluorescent, and since existing spectrophotometers are not suited to the evaluation of such samples, considerable reliance has been placed on quantitative colorimetric and photometric comparisons with the Munsell color standards, both by means of a chromaticity-difference colorimeter and by the Martens photometer. As a closing check Munsell book notations of these textile standards have been obtained by a direct visual comparison with the color scales of the Munsell Book of Color.

Recalibration of the NBS Glass Standards of Spectral Transmittance

In 1934, Gibson, Walker, and Brown developed sets of four colored glass filters to serve as working standards of spectral transmittance for checking the reliability of spectrophotometers. Several sets of these glasses were measured carefully and reserved and designated as future reference standards. Duplicate standards evaluated by comparison with the reference standards are available by purchase to the public. The current set of reference standards was established in the years 1945 to 1947, and one of these reference standards (selenium red) was recalibrated in 1952. This paper reports a recalibration, made in 1961 and 1962, of all four glasses (selenium red, carbon yellow, copper green, cobalt blue) on three spectrophotometers (Cary 14, Beckman DU, Konig–Martens). Except for the cobalt blue standard, the values of spectral transmittance found differ from those previously assigned by amounts differing at some wavelengths by as much as or slightly more than the uncertainties estimated for the present values, though not by amounts exceeding the combined uncertainties of the present and previous determinations. The indicated changes for these three standards are fairly regular, however, and support the view that the selenium red and carbon yellow standards are changing chiefly by formation of a reflectance-reducing film on the surfaces. The indicated rate of upward drift is slow, and suggests that it takes about 10 years for the drift to exceed the assigned uncertainty.

Specification of Railroad Signal Colors and Glasses

This paper is a continuation of RP1209 and describes the cooperative work done by the Association of American Railroads Signal Section, Corning Glass Works, and the National Bureau of Standards, leading to the formulation of the AAR Signal Section specifications for signal colors and glasses. The previous paper defined the luminous transmission scale used by the signal engineers and glass manufacturers. The present paper describes the glasses selected by these engineers to define the limits of acceptable chromaticities afforded by these glasses when combined with kerosene or electric illuminant. The spectral transmissions of the glasses are given, together with the luminous transmissions and chromaticities for the specified illuminants. The photometric and colorimetric parts of the AAR Signal Section three-part specifications are illustrated, and the reasons given for the choice of tolerances both on the acceptable signal colors and on the glasses certified by the National Bureau of Standards as duplicates of the standard limit glasses. Various other data of interest are given, including the expression of the permissible chromaticities of signal colors in a uniform-chromaticity-scale coordinate system.