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Journal of the Optical Society of America

Journal of the Optical Society of America

  • Vol. 30, Iss. 10 — Oct. 1, 1940
  • pp: 462–471

I. Fundamental Optical Properties

G. A. VAN LEAR, JR.  »View Author Affiliations

JOSA, Vol. 30, Issue 10, pp. 462-471 (1940)

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The present paper is the first of a series relating to the selection and use of such (reflex) reflectors as give night-time visibility to highway signs and act as warning signals on trucks, etc. The optical function common to the various types of such reflectors—retro-directive reflection—is described, and the manner of its accomplishment by each of the two general types is explained. Although descriptions of the inherent characteristics of all retro-directive reflectors indicate the conditions of use for best results, variations between reflectors of different types and different makes create need for quantitative descriptions of performance in terms suitable for specifications. Chief among the terms proposed for this purpose is specific intensity, which designates the candlepower of the reflector per footcandle illumination under specified conditions of illumination and viewing. Other special terms required for describing these conditions are proposed. There are brief preliminary discussions of test methods and interpretation of test results.

G. A. VAN LEAR, JR., "I. Fundamental Optical Properties," J. Opt. Soc. Am. 30, 462-471 (1940)

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  1. Retro-directive is a more appropriate term than auto-collimating, which has been widely used in this connection, particularly in the patent literature. Autocollimating has an accepted meaning which is quite different from the present one [see, e.g., R. A. Houstoun, A Treatise on Light (Longmans, Green and Company, 1930), p. 106]. The writer coined the term retro-directive reflector to fill the need for an accurately descriptive term, and used it in testimony in a patent suit before the Federal District Court in Dallas, Texas, during February, 1936. The trade term reflex reflector is perhaps satisfactory as such, but is not sufficiently descriptive for our purposes.
  2. A critical discussion of the applicability of this concept to such a situation will be given in Part II of this series of papers.
  3. R. Kingslake, J. Opt. Soc. Am. 28, 323 (1938).
  4. S. A. E. Handbook (Society of Automotive Engineers, 29 West 39th Street, New York, 1939), p. 611.

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