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Journal of the Optical Society of America

Journal of the Optical Society of America

  • Vol. 45, Iss. 7 — Jul. 1, 1955
  • pp: 525–528

Accuracy of the Macbeth Illuminometer as a Function of Operator Variability, Calibration, and Sensitivity

A. MORRIS, FREDERICK L. MCGUIRE, and HAROLD P. VAN COTT  »View Author Affiliations

JOSA, Vol. 45, Issue 7, pp. 525-528 (1955)

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The accuracy of the Macbeth illuminometer was studied by measuring a known source. The mean of a number of measurements from a number of operators gives a precise estimate of brightness. The most adequate measures are obtained when “calibration” amperage of the working lamp is carefully determined and maintained with precision.

To establish the relation between the sensitivity of the eye and brightness measurements; the difference thresholds for lighter and darker were determined. The close similarity of the curves for the threshold data and for the brightness measurements demonstrates that “match” judgments are essentially discriminations of “lighter” and “darker.”

A. MORRIS, FREDERICK L. MCGUIRE, and HAROLD P. VAN COTT, "Accuracy of the Macbeth Illuminometer as a Function of Operator Variability, Calibration, and Sensitivity," J. Opt. Soc. Am. 45, 525-528 (1955)

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  1. W. E. Middleton and A. R. Ramsey, Can. J. Research 26, 59–65 (1948).
  2. Bulb calibrated by Nati. Bur. Standards, Certificate No. 15P-48/49.
  3. Leeds and Northrup Company, Directions for No. 6801 Macbeth Illuminometers, Philadelphia, Pennsylvania.
  4. Illuminating Engineering Society, Committee on Lighting Practice, Trans. Illum. Eng. Soc. N. Y. 38, 75 (1943).
  5. The standard Macbeth illuminometer ammeter scale is marked every five ma; an ammeter with single ma unit markings was substituted.
  6. An exception to this generalization is operator VL. The average of his 10 preliminary calibration settings was 256.5 ma. The "X" value used was 257 ma. Correction of the "X" value by 0.5 ma would bring the data within the range of the source.
  7. See reference 1, p. 61.
  8. Projector, Laufer, and Douglas, Rev. Sci. Instr. 15, 107 (1944).

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