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Journal of the Optical Society of America

Journal of the Optical Society of America

  • Vol. 35, Iss. 12 — Dec. 1, 1945
  • pp: 772–795

Specification of Railroad Signal Colors and Glasses


JOSA, Vol. 35, Issue 12, pp. 772-795 (1945)

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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.

KASSON S. GIBSON, GERALDINE WALKER HAUPT, and HARRY J. KEEGAN, "Specification of Railroad Signal Colors and Glasses," J. Opt. Soc. Am. 35, 772-795 (1945)

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  1. Kasson S. Gibson and Geraldine Walker Haupt, "Standardization of the Luminous-Transmission Scale Used in the Specification of Railroad Signal Glasses," J. Research Nat. Bur. Stand. 22, 627 (1939) RP 1209, and J. Opt. Soc. Am. 29, 188 (1939).
  2. Standardization of railway signal glasses—Reports on measurements and investigations undertaken by the Colorimetry Section of the National Bureau of Standards at the request of the Signal Section, American Railway Association.Reports 1 to 5, published in Signal Section Proc., Am.Railway Assoc. 30, 384 (1933):Report 1. K. S. Gibson. The transmission (A.R.A. scale)of 36 specimens of signal glass relative to transmission of 6 A.R.A. standards marked "J. C. Mock 10-3-30," a report on measurements made at Corning Glass Works,December 9-11, 1930 (June 1, 1932).Report 2. K. S. Gibson and Geraldine K. Walker.Measurements of spectral and luminous transmissions leading to the derivation of new A.R.A. transmissions for the 36 glasses listed in report 1 (October 24, 1932).Report 3. Geraldine K. Walker and K. S. Gibson. Spectral and luminous transmissions and derivation of new values of A.R.A. transmission for the 22 "limit" glasses selected by committee VI, A.R.A., at Corning, November5-6, 1931, and engraved "J.C.M. 11-6-31" (December 2,1932).Report 4. K. S. Gibson and Geraldine K. Walker.Chromaticities and luminous transmissions, with illuminants at 1900'K and 28480K, for the 22 "limit" glasses described in Report 3 (January 30, 1933).Report 5. K. S. Gibson. Tentative specifications for railway signal colors (April 27, 1933).Reports 6 and 7. K. S. Gibson, Geraldine Walker Haupt,and H. J. Keegan, published in Signal Section Proc. Assoc.Am. Railroads 36, 136 (1939):Report 6. Examination of 65 duplicate limit glasses (July 26, 1934).Report 7. Colorimetric data leading to specification 59-38 for kerosene hand lantern globes; comparison of specifications 59-38, 69-38, and 69-35;certification ofduplicate lantern glasses (September 28, 1938).
  3. Specifications for Signal Roundels, Lenses, and Glass Slides. Proc. Railway Signal Assoc. 5 (1908). Railway Signal Association Specification 6918, Signal Roundels, Lenses, and Glass Slides (1918).
  4. Wm. Churchill, "The Roundel Problem," a paper presented at the Ninth Annual Meeting of the Railway Signal Association, Niagara Falls, New York, October 10–12, 1905.
  5. Optical Society of America Committee on Colorimetry, L. T. Troland, Chairman, "Report for 1920–21,"J. Opt. Soc. Am. and Rev. Sci. Inst. 6, 527 (1922).
  6. Proceedings Sixth Meeting, ICI, Geneva, p. 67 (1924). For résumé of recent work and present status of these ICI luminosity factors, see K. S. Gibson, "Spectral Luminosity Factors," J. Opt. Soc. Am. 30, 51 (1940).
  7. Proceedings Eighth Meeting, ICI, Cambridge, p. 19 (1931). D. B. Judd, "The 1931 ICI Standard Observer and Coordinate System for Colorimetry," J. Opt. Soc. Am. 23, 359 (1933). A. C. Hardy, Handbook of Colorimetry (The Technology Press, Cambridge, Massachusetts, 1936). "Quantitative Data and Methods for Colorimetry," Chapter VII of the forthcoming OSA Colorimetry Committee report, J. Opt. Soc. Am. 34, 633 (1944).
  8. H. P. Gage, "Practical Considerations in the Selection of Standards for Signal Glass in the United States," Proc., Intern. Cong. Illum., Saranac Inn, New York, p. 834 (1928).
  9. Specification 69 is entitled Signal Glasses (exclusive of kerosene hand lantern globes). It was published in essentially its present form in 1935, and was designated as 69-35. Slightly revised editions were published in 1938, 1939, and 1940, 69-40 being the current specification. Similarly specification 59 for kerosene hand lantern globes was published in essentially its present form in 1938, the current edition being designated as 59-39. Copies of these specifications are obtainable from Mr. R. H. C. Balliet, Secretary, AAR Signal Section, 30 Vesey Street, New York, New York.
  10. K. S. Gibson, Report No. 5, Tentative Specifications for Railway Signal Colors, Signal Section Proc., Am. Railway Assoc. 30, 429 (1933).
  11. See, for example, (1) Standards of the Institute of Traffic Engineers, Technical Report No. 1, Adjustable face traffic control signal head standards, 1940 Proceedings, (2) Bureau of Marine Inspection and Navigation (now part of U. S. Coast Guard), Proposed Specification covering navigation lights for vessels, alteration D (1941), (3) Army-Navy Aeronautical Specification: Colors; aeronautical lights and lighting equipment; AN-C-56 (1942); (4) Proceedings ICI, Tenth Session, Scheveningen, Holland (1939), condensed unofficial version edited and published by the United States National Committee, Figure 17.
  12. In describing these glasses the expressions "light limit" and "dark limit" have been retained because of their widespread use among signal engineers and glass manufacturers. The term, dark limit, is more or less appropriate but the term, light limit, is inappropriate since there is no upper limit of luminous transmission placed on any glassware in the specifications. The "light limit" glasses all define chromaticity limits, as indicated in Table II. Likewise, the values of TAAR.are given in the table because of their widespread usage in describing signal glasses.
  13. H. J. McNicholas, "Equipment for Routine Spectral Transmission and Reflection Measurements," Bur. Stand. J. Research 1, 793 (1928), RP 30.
  14. K. S. Gibson, "Direct-Reading Photoelectric Measurement of Spectral Transmission," J. Opt. Soc. Am. and Rev. Sci. Inst. 7, 693 (1923).
  15. As is well known, the exact values of radiant energy for any specified temperature depend on the value of C2 in Planck's equation [Equation] For continuity with the published reports and specifications we are retaining the value of C2 =: 14,350 microndegrees. Recent values have varied from 14,320 on the International temperature scale to 14,360 as recommended by Wensel, J. Research Nat. Bur. Stand. 22, 375 (1939) RP 1189. All values of color temperature in this paper are based on C2 = 14,350.
  16. In Figs. 7, 8, and 13, certain of the numbers designating the blue and purple glasses carry the auxiliary designations B or P, as engraved on the glasses. In the rest of the paper, however, these letters have been omitted, since they seemed unnecessary and somewhat confusing.
  17. This boundary was originally at y = 0.3 86 given by 142 with kerosene illuminant, but was later lowered to y = 0.384 to include the red limit of lantern yellow No. 271.
  18. Because of chromatic aberration of the lens system of the human eye, the dichromatic image is normally a red center with a blue halo or surround, though this will vary with the vision of the observer. Neither blue nor purple are used as long range, high speed signals.
  19. Lunar white glasses are "cobalt blue" glasses. Experience indicates that important deviations in the green or purple directions do not occur in the manufacture of such glasses.
  20. Army-Navy Aeronautical Specification: Colors; Aeronautical Lights and Lighting Equipment; AN-C-56 (1942).
  21. See references 721–731 of chapter VII, "Quantitative Data and Methods for Colorimetry," of the forthcoming report of the OSA Committee on Colorimetry, J. Opt. Soc. Am. 34, 633 (1944).
  22. Deane B. Judd, "A Maxwell Triangle Yielding Uniform Chromaticity Scales," J. Research Nat. Bur. Stand. 14, 41 (1935) RP 756; J. Opt. Soc. Am. 25, 24 (1935).
  23. Deane B. Judd, "Estimation of Chromaticity Differences and Nearest Color Temperature on the Standard 1931 ICI Colorimetric Coordinate System," J. Research Nat. Bur. Stand. 17, 771 (1936) RP 944; J. Opt. Soc. Am. 26, 421 (1936).
  24. That is, inside-frosted incandescent lamps.
  25. Many of the glasses certified by the National Bureau of Standards have been prepared by Corning Glass Works without charge. Under present arrangements such glasses may be purchased from Corning Glass Works for a nominal amount and certified by the National Bureau of Standards at regular test fee schedules. The Bureau will also accept suitable glasses from other companies for test, with the regular charge for certification or rejection.

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