Metrology of fluorescent retroreflective materials and its relationship totheir daytime visibility

lThis paper describes aspects of fluorescence that relate to high-visibilit y retroreflective materials used for visual signaling and markings. Full co lorimetric characterization of these materials requires separation of the f luorescent 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 applicatio ns. When measuring retroreflective materials, it has been found that measur ement geometry has a significant influence on the reflected spectral radian ce factors. For fluorescent retroreflective materials, the reflected compon ent is more sensitive than the fluorescent component to geometric restraint s. Therefore, geometric specifications and tolerances are critical in the m easurement of these materials. Assessment of the relative visibility and conspicuity of fluorescent materi als requires an understanding of the relationship between the spectral illu mination and the total luminance factor of the specimen. Precise calculatio n of the total luminance factor under the varying conditions of illuminatio n encountered in outdoor signing and marking applications is possible using the complete bispectral radiance factor array. The relationship between ca lculated results and field measurements is described. For routine quality c ontrol and material specification a more abridged metrology making use of t he fluorescence luminance factor (Y-F) has been found useful. Y-F for CIE i lluminant D65 can be used to assess the fluorescent content and durability of fluorescent materials used in signing applications. Y-F has also been fo und to correlate with the increased visibility performance of fluorescent s igns under poor daytime visibility conditions. The introduction of Y-F into materials specifications is beginning to take place; (C) 1999 Published by Elsevier Science B.V. All rights reserved.