scope:

Introduction

Flashing lights are widely used in many signalling applications in aviation, marine and land transportation. Flashing lights, such as aircraft anti-collision lights, marine aid-to-navigation lights, obstruction lights and emergency vehicle warning lights, are specified by their effective intensity (in candelas). These lights need to be measured and the effective intensity calculated to ensure that they meet specifications. Several different formulae have historically been used to determine the effective intensity. When these different formulae are applied to a given flash, their results often disagree. Development of a single standard method is desirable.

This Technical Report provides a groundwork for developing a recommendation on determination of effective intensity of flashing lights. It recommends a convolutional method that will rest on some defined visual impulse response function to calculate the effective intensity. As one of such realizations of convolutional methods, the Modified Allard Method with an infinite time window is described. However, it is not yet an official recommendation due to the lack of experimental verification and the need for further research.

This Technical Report also provides guidance on physical measurements of effective intensity, dealing with flashing lights with pulse widths in the range from microseconds to seconds. Xenon flash sources are commonly used, but recently LEDs are increasingly used for signalling sources. Some examples of the waveform of flashing light sources are shown in Figure 1. Gaussian flash profiles are also seen in aeronautical and marine beacons employing rotating optics.