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.
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)