Messgeometrien für die Bewertung der Nachtsichtbarkeit von retroreflektierenden Materialien bezüglich der Rückstrahleigenschaften
This document has been prepared by Joint Working Committee NA 025-00-25 GA "Gemeinschaftsarbeitsausschuss FNF/FNL: Aufsichtfarben für Verkehrszeichen und Reflexstoffe zur Verkehrssicherung" ("Joint working committee FNF/FNL: Surface colours for traffic signs and retroreflective sheeting materials for traffic safety purposes") of the Colour Standards Committee (FNF) at DIN. This document summarizes the current state of discussion and shall be supplemented in terms of content at a later date. Until now, the requirements for the visual quality of traffic signs have mainly been specified on the basis of investigations that are more than 20 years old. Due to the higher traffic volume, visual impairment caused by the headlights of approaching vehicles in the dark has significantly increased. Traffic signs are rivalled in their conspicuousness by an increasing number of illuminated advertisements and billboards put up along the roads. The number of light sources that do not pertain to traffic, such as the illumination of buildings or stadiums, has increased significantly. Therefore it has become necessary to take these changed influences into consideration and to ensure and improve the recognisability of traffic signs by suitable requirements for the retroreflective materials. The purpose of this publication is the redefinition of measuring geometries for assessing retroreflective materials. The assessment of the night visibility of retroreflective materials for use in vertical traffic signs is currently limited to the measurement of the specific coefficients of luminous intensity RA, which are required to fulfil certain minimum values, for instance in accordance with DIN 67520 and the technical delivery conditions and test conditions for vertical traffic signs (TLP VZ) for specified measuring angles. These measuring angles only represent, however, illumination and observation geometries as they occur in street traffic areas in a limited fashion. For now, the influences of the rotation angles on the specific coefficient of luminous intensity are insufficiently considered. This is particularly problematic for the assessment of rotationally asymmetric materials, for instance microprismatic types. In clauses 2 and 3 important terms for the particular subject as well as the lighting technology and geometric principles are described, while clause 4 deals with the different superstructures of the retroreflective materials. Clause 5 derives typical assemblies of traffic signs for streets with two or three carriageways. Clause 6 deals with vehicle-specific data and the different luminous intensity distribution of vehicle headlights. Clause 7 specifies the distance and angle dimensions, from which the angles for a future measurement and assessment of retroreflective materials are derived in clause 8. Clause 9 includes the angles necessary for the measurement execution with the CIE goniometer and describes the evaluation of the measurement data. Clause 10 gives the links between the results from this document and the national and European standards. The results of this work can serve as the foundation for a revision of the set of rules for assessment of the suitability of retroreflective materials for vertical street signs.