Abstract

This paper describes a method of measuring the apparent change in the intensity of a beacon as its rate of rotation is altered. The equivalent intensity of several beacons is plotted against the duration of the flash. It is found that Blondel and Rey’s law for abrupt flashes also seems to describe the equivalent intensity of service beacons to a first degree of approximation.

© 1938 Optical Society of America

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References

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  1. An investigation carried out for the Bureau of Air Commerce, of the U. S. Department of Commerce, by the National Bureau of Standards and described in detail in a report being issued by the Safety and Planning Division, Bureau of Air Commerce. Publication of this paper approved by the Director of the Bureau of Air Commerce.
  2. Publication approved by the Director of the National Bureau of Standards of the U. S. Department of Commerce.
  3. The word visibility, as used in this paper, refers to the capacity of a light source to stand out from the background, i.e., the contrast between the light source and the background. Other words which have this connotation are discernability, visiopia, and visability. Visibility is chosen because it is the more common synonym and hence less likely to confuse the reader.
  4. A. Blondel and J. Rey, Comptes rendus 153, 54 (1911); Comptes rendus 162, 587 and 861 (1916); Comptes rendus 178, 276 and 1245 (1924).
  5. H. Piéron, Comptes rendus 170, 525 and 1203 (1920); Comptes rendus 178, 276, 966 and 1245 (1924).
  6. A. K. Toulmin-Smith and H. N. Green, “The Fixed Light Equivalent of Flashing Lights,” Illum. Eng. 26, 304 (1933).
  7. P. Van Braam Van Vloten, L’Élairage des Routes Aériennes, Ve Congrés Internationale de la Navigation Aerienne (1930), p. 5.
  8. I. Langmuir and W. F. Westendorp, “A Study of Light Signals in Aviation and Navigation,” Physics 1, 273 (1931).
    [Crossref]
  9. W. M. Hampton, “The Fixed Light Equivalent of Flashing Lights,” Illum. Eng. 27, 46 (1934).
  10. For Ee near the threshold level, Toulmin-Smith and Green obtained k = 0.2 second. Therefore, a flash-duration of about 4 seconds would be required to give an apparent-intensity ratio of 95 percent under these conditions.
  11. Conclusion (2) states that, in general, the equivalent intensity of a flash is not directly proportional to its luminous energy, J, but depends upon the duration, t–the shorter the duration, the greater the effect per unit of luminous energy. This result follows also from Eq. (1), for abrupt flashes. Since:JαIt,JαIe(k+t),where Ie = a constant, since, in Blondel and Rey’s experiments, it is held at the observer’s threshold and in Toulmin-Smith and Green’s experiments it is held constant at various levels. Thus, the energy required for constant visibility is a linear function of the duration of the flash, the longer flashes requiring more energy and hence being less effective per unit of visual energy. This corresponds to a lowered retinal sensitivity for the long flashes.

1934 (1)

W. M. Hampton, “The Fixed Light Equivalent of Flashing Lights,” Illum. Eng. 27, 46 (1934).

1933 (1)

A. K. Toulmin-Smith and H. N. Green, “The Fixed Light Equivalent of Flashing Lights,” Illum. Eng. 26, 304 (1933).

1931 (1)

I. Langmuir and W. F. Westendorp, “A Study of Light Signals in Aviation and Navigation,” Physics 1, 273 (1931).
[Crossref]

1930 (1)

P. Van Braam Van Vloten, L’Élairage des Routes Aériennes, Ve Congrés Internationale de la Navigation Aerienne (1930), p. 5.

1920 (1)

H. Piéron, Comptes rendus 170, 525 and 1203 (1920); Comptes rendus 178, 276, 966 and 1245 (1924).

1911 (1)

A. Blondel and J. Rey, Comptes rendus 153, 54 (1911); Comptes rendus 162, 587 and 861 (1916); Comptes rendus 178, 276 and 1245 (1924).

Blondel, A.

A. Blondel and J. Rey, Comptes rendus 153, 54 (1911); Comptes rendus 162, 587 and 861 (1916); Comptes rendus 178, 276 and 1245 (1924).

Green, H. N.

A. K. Toulmin-Smith and H. N. Green, “The Fixed Light Equivalent of Flashing Lights,” Illum. Eng. 26, 304 (1933).

Hampton, W. M.

W. M. Hampton, “The Fixed Light Equivalent of Flashing Lights,” Illum. Eng. 27, 46 (1934).

Langmuir, I.

I. Langmuir and W. F. Westendorp, “A Study of Light Signals in Aviation and Navigation,” Physics 1, 273 (1931).
[Crossref]

Piéron, H.

H. Piéron, Comptes rendus 170, 525 and 1203 (1920); Comptes rendus 178, 276, 966 and 1245 (1924).

Rey, J.

A. Blondel and J. Rey, Comptes rendus 153, 54 (1911); Comptes rendus 162, 587 and 861 (1916); Comptes rendus 178, 276 and 1245 (1924).

Toulmin-Smith, A. K.

A. K. Toulmin-Smith and H. N. Green, “The Fixed Light Equivalent of Flashing Lights,” Illum. Eng. 26, 304 (1933).

Van Braam Van Vloten, P.

P. Van Braam Van Vloten, L’Élairage des Routes Aériennes, Ve Congrés Internationale de la Navigation Aerienne (1930), p. 5.

Westendorp, W. F.

I. Langmuir and W. F. Westendorp, “A Study of Light Signals in Aviation and Navigation,” Physics 1, 273 (1931).
[Crossref]

Comptes rendus (2)

A. Blondel and J. Rey, Comptes rendus 153, 54 (1911); Comptes rendus 162, 587 and 861 (1916); Comptes rendus 178, 276 and 1245 (1924).

H. Piéron, Comptes rendus 170, 525 and 1203 (1920); Comptes rendus 178, 276, 966 and 1245 (1924).

Illum. Eng. (2)

A. K. Toulmin-Smith and H. N. Green, “The Fixed Light Equivalent of Flashing Lights,” Illum. Eng. 26, 304 (1933).

W. M. Hampton, “The Fixed Light Equivalent of Flashing Lights,” Illum. Eng. 27, 46 (1934).

L’Élairage des Routes Aériennes, Ve Congrés Internationale de la Navigation Aerienne (1)

P. Van Braam Van Vloten, L’Élairage des Routes Aériennes, Ve Congrés Internationale de la Navigation Aerienne (1930), p. 5.

Physics (1)

I. Langmuir and W. F. Westendorp, “A Study of Light Signals in Aviation and Navigation,” Physics 1, 273 (1931).
[Crossref]

Other (5)

For Ee near the threshold level, Toulmin-Smith and Green obtained k = 0.2 second. Therefore, a flash-duration of about 4 seconds would be required to give an apparent-intensity ratio of 95 percent under these conditions.

Conclusion (2) states that, in general, the equivalent intensity of a flash is not directly proportional to its luminous energy, J, but depends upon the duration, t–the shorter the duration, the greater the effect per unit of luminous energy. This result follows also from Eq. (1), for abrupt flashes. Since:JαIt,JαIe(k+t),where Ie = a constant, since, in Blondel and Rey’s experiments, it is held at the observer’s threshold and in Toulmin-Smith and Green’s experiments it is held constant at various levels. Thus, the energy required for constant visibility is a linear function of the duration of the flash, the longer flashes requiring more energy and hence being less effective per unit of visual energy. This corresponds to a lowered retinal sensitivity for the long flashes.

An investigation carried out for the Bureau of Air Commerce, of the U. S. Department of Commerce, by the National Bureau of Standards and described in detail in a report being issued by the Safety and Planning Division, Bureau of Air Commerce. Publication of this paper approved by the Director of the Bureau of Air Commerce.

Publication approved by the Director of the National Bureau of Standards of the U. S. Department of Commerce.

The word visibility, as used in this paper, refers to the capacity of a light source to stand out from the background, i.e., the contrast between the light source and the background. Other words which have this connotation are discernability, visiopia, and visability. Visibility is chosen because it is the more common synonym and hence less likely to confuse the reader.

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Figures (4)

Fig. 1
Fig. 1

Horizontal intensity distribution in the edges of the beam of the 18-inch beacon.

Fig. 2
Fig. 2

Equivalent-intensity ratio in percent as a function of the period of rotation of the 24-inch beacon.

Fig. 3
Fig. 3

Equivalent-intensity ratio in percent as a function of the period of rotation of the 18-inch beacon.

Fig. 4
Fig. 4

Equivalent-intensity ratios in percent plotted against the nominal duration of the flash in seconds. The curves represent Blondel and Rey’s law.

Tables (3)

Tables Icon

Table I Data for the 24-inch beacon.

Tables Icon

Table II Data for the 18-inch beacon. Except as stated below, all values of Ie/I are for the (double-ended) beacon with one face covered, for a clear flash, and for an observation distance of 8 miles.

Tables Icon

Table III Relation of equivalent-intensity ratio to flash duration for various beacons.

Equations (4)

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I e / I = t / ( k + t ) ,
I e / I = K t / ( k + t ) .
k = ( 0.0255 / E c ) 0.81 .
JαIt,JαIe(k+t),