Geraldine Walker Haupt

An Alkaline Solution of Potassium Chromate as a Transmittancy Standard in the Ultraviolet

The need for a means of testing the reliability of the photometric scale of spectrophotometers in the ultraviolet region (where glasses are unsuitable) has led to the study of an aqueous solution of potassium chromate having the following composition: 0.0400 gram per liter of K2CrO4 in 0.05 N KOH. Based on extensive measurements using photographic, photoelectric, and visual spectrophotometry, standard values of spectral transmittancy have been determined for 1.000 and 2.000 cm of solution at 25°C from 220 to 500 mμ. These values have been tabulated along with derived values of absorbancy, molar absorbancy index aM, and log10aM. The latter values have been compared graphically with those of other observers. Changes in spectral transmittancy with changes in temperature have been determined. The investigation has also included a study of the effects due to the container bottle and to age of solutions over periods up to eight years, and a comparison of results obtained with the solution prepared either from K2CrO4 or from K2Cr2O7 as one of the reagents.

Spectral Energy Distribution of the International Commission on Illumination Light Sources A, B, and C*

Standard light sources A, B, and C were adopted by the International Commission on Illumination (C.I.E.) in 1931 for the colorimetry of materials. Source A is an incandescent lamp operated at 2854°K. Sources B and C, representative of average noon sunlight and average daylight, respectively, are produced by passing radiant flux from source A through specified Davis-Gibson filters described in Bureau of Standards Miscellaneous Publication M114 (1931).The C.I.E. published relative energy data only from 370 to 720 mµ. The present paper gives data for these sources in the ultraviolet and extends the data in the red to 780 mµ. The new data were reported through the U. S. Secretariat Committee to the C.I.E. at its 1951 meeting. The values in the ultraviolet were reported to the Optical Society of America at its March, 1952, meeting.

Chromaticities of Lovibond Glasses

This paper reports by means of a series of graphs the chromaticity coordinates of certain Lovibond unit glasses and of pairs of such glasses in combination with an illuminant of color temperature 2842°K (Illuminant A). The chromaticities were computed according to the 1931 I.C.I. standard observer and coordinate system. The points graphically representing the x and y values have been labelled according to the Lovibond numbers and have been connected by lines to form a network. A similar graph is included for a few Lovibond glasses in combination with Illuminant C. The Lovibond glasses are those from the NBS set designated as “BS9940,” and the spectrophotometric data on which the colorimetric computations are based are those published by Gibson and Harris.

Standardization of the Luminous Transmission Scale Used in the Specification of Railroad Signal Glasses

This is the first of several papers dealing with the development and description of the signal glass specifications formulated by the Signal Section of the Association of American Railroads in 1935 and 1938. The present paper gives the spectral transmissions of the basic standards—red, yellow, green, blue, purple and lunar white glasses—on which the A. A. R. scale of luminous transmission is based, and defines that scale in fundamental, absolute units. Comparison is made with the scales defined in the 1908 and 1918 signal glass specifications.

Ideal Lovibond Color System

Lovibond red, yellow, and blue glasses, widely used as color standards in industry, are assigned numerals in accord with the basic plan of marking each glass with the number of unit glasses of the same type through which light must be passed to produce its color. It is possible to compute from the spectral transmittances of the unit glasses defining the Lovibond scales the CIE specification of the color produced by all combinations of any number of unit glasses. Such specifications were computed in 1939 not only for all ideal red, yellow, and blue Lovibond glasses illuminated by CIE sources B (representing noon sunlight) or C (representing average daylight) but also for two-part (red-yellow, yellow-blue, or blue-red) combinations thereof. The present paper gives the results of such computations for CIE source A (representing gas-filled incandescent lamps). Although actual Lovibond glasses must unavoidably depart somewhat from this definition of the ideal Lovibond system, the computed color specifications serve to indicate with good reliability not only the CIE specification of the color produced by single glasses and two-part combinations, but also the choice of Lovibond glasses required to produce a color of any desired chromaticity within the gamut of the system.

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.