Metrology of fluorescent retroreflective materials and its relationship to their daytime visibility

Abstract This paper describes aspects of fluorescence that relate to high-visibility retroreflective materials used for visual signaling and markings. Full colorimetric characterization of these materials requires separation of the fluorescent and non-fluorescent components. Quantification of the individual components allows for accurate prediction of performance under the various conditions of illumination and viewing encountered in practical applications. When measuring retroreflective materials, it has been found that measurement geometry has a significant influence on the reflected spectral radiance factors. For fluorescent retroreflective materials, the reflected component is more sensitive than the fluorescent component to geometric restraints. Therefore, geometric specifications and tolerances are critical in the measurement of these materials. Assessment of the relative visibility and conspicuity of fluorescent materials requires an understanding of the relationship between the spectral illumination and the total luminance factor of the specimen. Precise calculation of the total luminance factor under the varying conditions of illumination encountered in outdoor signing and marking applications is possible using the complete bispectral radiance factor array. The relationship between calculated results and field measurements is described. For routine quality control and material specification a more abridged metrology making use of the fluorescence luminance factor (YF) has been found useful. YF for CIE illuminant D65 can be used to assess the fluorescent content and durability of fluorescent materials used in signing applications. YF has also been found to correlate with the increased visibility performance of fluorescent signs under poor daytime visibility conditions. The introduction of YF into materials specifications is beginning to take place.