Abstract

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.”

© 1955 Optical Society of America

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References

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  1. W. E. Middleton and A. R. Ramsey, Can. J. Research 26, 59–65 (1948).
    [Crossref]
  2. Bulb calibrated by Natl. 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).
    [Crossref]

1948 (1)

W. E. Middleton and A. R. Ramsey, Can. J. Research 26, 59–65 (1948).
[Crossref]

1944 (1)

Projector, Laufer, and Douglas, Rev. Sci. Instr. 15, 107 (1944).
[Crossref]

1943 (1)

Illuminating Engineering Society, Committee on Lighting Practice, Trans. Illum. Eng. Soc. N. Y. 38, 75 (1943).

Douglas,

Projector, Laufer, and Douglas, Rev. Sci. Instr. 15, 107 (1944).
[Crossref]

Laufer,

Projector, Laufer, and Douglas, Rev. Sci. Instr. 15, 107 (1944).
[Crossref]

Middleton, W. E.

W. E. Middleton and A. R. Ramsey, Can. J. Research 26, 59–65 (1948).
[Crossref]

Projector,

Projector, Laufer, and Douglas, Rev. Sci. Instr. 15, 107 (1944).
[Crossref]

Ramsey, A. R.

W. E. Middleton and A. R. Ramsey, Can. J. Research 26, 59–65 (1948).
[Crossref]

Can. J. Research (1)

W. E. Middleton and A. R. Ramsey, Can. J. Research 26, 59–65 (1948).
[Crossref]

Rev. Sci. Instr. (1)

Projector, Laufer, and Douglas, Rev. Sci. Instr. 15, 107 (1944).
[Crossref]

Trans. Illum. Eng. Soc. N. Y. (1)

Illuminating Engineering Society, Committee on Lighting Practice, Trans. Illum. Eng. Soc. N. Y. 38, 75 (1943).

Other (5)

The standard Macbeth illuminometer ammeter scale is marked every five ma; an ammeter with single ma unit markings was substituted.

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.

See reference 1, p. 61.

Bulb calibrated by Natl. Bur. Standards, Certificate No. 15P-48/49.

Leeds and Northrup Company, Directions for No. 6801 Macbeth Illuminometers, Philadelphia, Pennsylvania.

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Figures (7)

Fig. 1
Fig. 1

Frequency distribution of Macbeth illuminometer measurements by five operators.

Fig. 2
Fig. 2

Individual frequency distributions of brightness measurements by five operators.

Fig. 3
Fig. 3

Session-to-session variability shown by means and ranges of groups of ten measurements.

Fig. 4
Fig. 4

Field brightness measurements at various current settings, sample data for one observer.

Fig. 5
Fig. 5

Brightness measurements at various current settings.

Fig. 6
Fig. 6

Difference limens under calibrating condition for Macbeth illuminometer.

Fig. 7
Fig. 7

Comparison of psychophysical limens with brightness measurements.

Tables (4)

Tables Icon

Table I Percentages of total brightness measurements falling within deviation ranges.

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Table II Percent of measurements made by each operator falling within deviation ranges.

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Table III Probability that the mean of any five successive measurements will fall within specified limits.

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Table IV Threshold data taken under calibrating conditions for the Macbeth illuminometer.