5.1 The quantity coefficient of retroreflected luminance is a measure of the reflected luminance in the direction of the observer. This is the light returned by the retroreflective surface to the observer from the source, which in practice is the vehicle headlamp.

5.2 This test method may be used as a measure of the nighttime performance of horizontally applied surfacing materials used on highway surfaces for lane markings and other traffic control purposes.

5.3 Since this test method is a laboratory procedure, test specimens must be prepared so that they can be mounted on the specimen holder. Specimens measured by this laboratory method may be used as transfer standards for the calibration of portable instrumentation.

5.4 Specimen selection and preparation may significantly influence the results of this test method.

1.1 This test method describes the instrumental measurement of the retroreflective properties of horizontal surfacing materials, such as traffic stripe paint systems, traffic tapes, and traffic surface symbols.

1.2 Specimen preparation, size, and shape must be determined and specified by the user of this test method. Likewise, the user must specify the observation and entrance angles to be used (see Fig. 1).

FIG. 1 Diagram Illustrating Geometry for Measurement of Horizontal Coatings Specimens

Note 1: Includes observation angle α, entrance angle β, viewing angle ν_a, co-viewing angle ν_c, and co-entrance angle β_c. The retroreflector axis, illumination axis, and observation axis all lie in the same plane.

1.3 The geometric requirements of this test method are based on materials for which the relative retroreflectance changes less than approximately 50 % over the observation angle range from 0.2 to 0.5°. This is illustrated in Fig. 2.

FIG. 2 Illustration of Typical Rate of Change of Retroreflectance Versus Observation Angle for Horizontal Retroreflective Material Measured at 86° Entrance Angle

1.4 This test method is a laboratory test and requires a facility that can be darkened sufficiently so that stray light does not affect the test results. This facility must be capable of housing the required 15-m test distance.

1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.