Gerald Kent Neeland, Maurice K. Laufer, and Wallace R. Schaub, "Measurement of the Equivalent Luminous Intensity of Rotating Beacons1,2," J. Opt. Soc. Am. 28, 280-285 (1938)
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.
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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.
Equivalent-Intensity Ratio, Ie/I, in %, at Periods (Seconds) Indicated Below
Notes:
Weighted by the number of observers,
Threshold varied during test between the limits indicated.
Red (inner) lens used, thus giving a red flash.
Observed from a distance of 3 miles—the threshold value corresponds to about 300 candles at 8 miles under the same conditions.
Both faces of beacon exposed, thus doubling the flash frequency without changing the duration of the flash.
Table III
Relation of equivalent-intensity ratio to flash duration for various beacons.
1
2
3
4
5
Type of Beacon
Equivalent-Intensity Ratio at Periods Indicated (Seconds)
Beam Spread
Nominal Duration of Flash for the Periods Indicated (Seconds)
Calculated Values ofkfor the Periods Indicated (Seconds)
The 24-inch and 18-inch beacons were observed from a distance of 8 miles. (Values given are weighted means from Tables I and II.) The other three were observed from a distance of 3 miles.
Tables (3)
Table I
Data for the 24-inch beacon.
Test Number
Date
Average Threshold Intensity (Candles)
Number of Observers
Equivalent-Intensity Ratio, Ie/I, in %. at Periods (Seconds) Indicated Below
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.
Equivalent-Intensity Ratio, Ie/I, in %, at Periods (Seconds) Indicated Below
Notes:
Weighted by the number of observers,
Threshold varied during test between the limits indicated.
Red (inner) lens used, thus giving a red flash.
Observed from a distance of 3 miles—the threshold value corresponds to about 300 candles at 8 miles under the same conditions.
Both faces of beacon exposed, thus doubling the flash frequency without changing the duration of the flash.
Table III
Relation of equivalent-intensity ratio to flash duration for various beacons.
1
2
3
4
5
Type of Beacon
Equivalent-Intensity Ratio at Periods Indicated (Seconds)
Beam Spread
Nominal Duration of Flash for the Periods Indicated (Seconds)
Calculated Values ofkfor the Periods Indicated (Seconds)
The 24-inch and 18-inch beacons were observed from a distance of 8 miles. (Values given are weighted means from Tables I and II.) The other three were observed from a distance of 3 miles.
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