Characterising the effective intensity of multiple-pulse flashing signal lights

Flashing lights used in aviation signal applications can be characterised by the luminous intensity of a steady-burning signal light with the same visual effectiveness. Different formulae exist for calculating the effective intensity of flashing signal lights that use multiple brief pulses of light within each flash. The results of a laboratory study conducted to test these calculation methods revealed that a formulation based on the Blondel-Rey-Douglas effective intensity method was more predictive of judgments of overall visibility than a different formulation published in recent aviation authority guidance. A follow-up experiment yielded confirmation of these findings. Different aspects of visibility resulted in very different judgments, and the limitations of the effective intensity concept to characterise the visibility of a flashing light are also discussed.