4.1 This practice applies to any measurement of reflectance in which the angle at the sample between the direction of the incident radiation and the direction of viewing is less than approximately 10°, and the reflected radiation is concentrated in a direction opposite to the direction of incidence.

4.2 The CIE (goniometer) system described in 6.1.1 was developed by the Subcommittee on Retroreflection of Committee 2.3 on Materials of the International Commission on Illumination (Commission International de l'Eclairage, CIE). It is intended to provide a common basis for the measurement of retroreflection, which should be used worldwide.

4.3 This practice provides alternative geometric coordinate systems useful for visualizing relationships between various angles in actual use.

1.1 This practice provides terminology, alternative geometrical coordinate systems, and procedures for designating angles in descriptions of retroreflectors, specifications for retroreflector performance, and measurements of retroreflection.

1.2 Terminology defined herein includes terms germane to other ASTM documents on retroreflection.

1.3 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 and health practices and determine the applicability of regulatory limitations prior to use.