Effective Intensity of Multiple-Pulse Flashing Signal Lights

Historically, a steady light is quantified by intensity, and a flashing light is quantified by effective intensity. Experts in the lighting industry speculate that the equation specified by the Federal Aviation Administration (FAA) in Advisory Circular (AC) 150/5345-43H is not the most accurate way to determine the effective intensity of flashing lights. Flashing lights used in aviation signal applications can be characterized by the luminous intensity of a steady-burning signal light with the same visual effectiveness. Different formulas exist to calculate the effective intensity of flashing signal lights that use multiple brief pulses of light within each flash. This research effort was initiated to develop a more accurate way to compute effective intensity. In 2011, a laboratory study was conducted to test these calculation methods. The study revealed that a formula based on the Blondel-Rey effective intensity method, proposed by Douglas, was more predictive of judgments of overall visibility than the formula currently published in the FAA AC. A follow-up experiment confirmed that the current FAA equation should be updated to the Blondel-Rey-Douglas formula. In this report, different visibility aspects resulted in very different judgments, and the limitations of the effective intensity concept to characterize the visibility of flashing lights are discussed.

DOT/FAA/TC-17/49
Authors: Bullough, J.D, Skinner, N.P., and Taranta, R.